Merge branch 'scv' support into next

From Nick's cover letter:

Linux powerpc new system call instruction and ABI

System Call Vectored (scv) ABI
==============================

The scv instruction is introduced with POWER9 / ISA3, it comes with an
rfscv counter-part. The benefit of these instructions is
performance (trading slower SRR0/1 with faster LR/CTR registers, and
entering the kernel with MSR[EE] and MSR[RI] left enabled, which can
reduce MSR updates. The scv instruction has 128 levels (not enough to
cover the Linux system call space).

Assignment and advertisement
----------------------------
The proposal is to assign scv levels conservatively, and advertise
them with HWCAP feature bits as we add support for more.

Linux has not enabled FSCR[SCV] yet, so executing the scv instruction
will cause the kernel to log a "SCV facility unavilable" message, and
deliver a SIGILL with ILL_ILLOPC to the process. Linux has defined a
HWCAP2 bit PPC_FEATURE2_SCV for SCV support, but does not set it.

This change allocates the zero level ('scv 0'), advertised with
PPC_FEATURE2_SCV, which will be used to provide normal Linux system
calls (equivalent to 'sc').

Attempting to execute scv with other levels will cause a SIGILL to be
delivered the same as before, but will not log a "SCV facility
unavailable" message (because the processor facility is enabled).

Calling convention
------------------
The proposal is for scv 0 to provide the standard Linux system call
ABI with the following differences from sc convention[1]:

- LR is to be volatile across scv calls. This is necessary because the
  scv instruction clobbers LR. From previous discussion, this should
  be possible to deal with in GCC clobbers and CFI.

- cr1 and cr5-cr7 are volatile. This matches the C ABI and would allow
  the kernel system call exit to avoid restoring the volatile cr
  registers (although we probably still would anyway to avoid
  information leaks).

- Error handling: The consensus among kernel, glibc, and musl is to
  move to using negative return values in r3 rather than CR0[SO]=1 to
  indicate error, which matches most other architectures, and is
  closer to a function call.

Notes
-----
- r0,r4-r8 are documented as volatile in the ABI, but the kernel patch
  as submitted currently preserves them. This is to leave room for
  deciding which way to go with these. Some small benefit was found by
  preserving them[1] but I'm not convinced it's worth deviating from
  the C function call ABI just for this. Release code should follow
  the ABI.

Previous discussions:
https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/208691.html
https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/209268.html

[1] https://github.com/torvalds/linux/blob/master/Documentation/powerpc/syscall64-abi.rst
[2] https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/209263.html

Documentation/powerpc/syscall64-abi.rst

@@ -5,6 +5,15 @@ Power Architecture 64-bit Linux system call ABI
 syscall
 =======
 
+Invocation
+----------
+The syscall is made with the sc instruction, and returns with execution
+continuing at the instruction following the sc instruction.
+
+If PPC_FEATURE2_SCV appears in the AT_HWCAP2 ELF auxiliary vector, the
+scv 0 instruction is an alternative that may provide better performance,
+with some differences to calling sequence.
+
 syscall calling sequence\ [1]_ matches the Power Architecture 64-bit ELF ABI
 specification C function calling sequence, including register preservation
 rules, with the following differences.
@@ -12,16 +21,23 @@ rules, with the following differences.
 .. [1] Some syscalls (typically low-level management functions) may have
        different calling sequences (e.g., rt_sigreturn).
 
-Parameters and return value
----------------------------
+Parameters
+----------
 The system call number is specified in r0.
 
 There is a maximum of 6 integer parameters to a syscall, passed in r3-r8.
 
-Both a return value and a return error code are returned. cr0.SO is the return
-error code, and r3 is the return value or error code. When cr0.SO is clear,
-the syscall succeeded and r3 is the return value. When cr0.SO is set, the
-syscall failed and r3 is the error code that generally corresponds to errno.
+Return value
+------------
+- For the sc instruction, both a value and an error condition are returned.
+  cr0.SO is the error condition, and r3 is the return value. When cr0.SO is
+  clear, the syscall succeeded and r3 is the return value. When cr0.SO is set,
+  the syscall failed and r3 is the error value (that normally corresponds to
+  errno).
+
+- For the scv 0 instruction, the return value indicates failure if it is
+  -4095..-1 (i.e., it is >= -MAX_ERRNO (-4095) as an unsigned comparison),
+  in which case the error value is the negated return value.
 
 Stack
 -----
@@ -34,22 +50,23 @@ Register preservation rules match the ELF ABI calling sequence with the
 following differences:
 
 =========== ============= ========================================
+--- For the sc instruction, differences with the ELF ABI ---
 r0          Volatile      (System call number.)
 r3          Volatile      (Parameter 1, and return value.)
 r4-r8       Volatile      (Parameters 2-6.)
-cr0         Volatile      (cr0.SO is the return error condition)
+cr0         Volatile      (cr0.SO is the return error condition.)
 cr1, cr5-7  Nonvolatile
 lr          Nonvolatile
+
+--- For the scv 0 instruction, differences with the ELF ABI ---
+r0          Volatile      (System call number.)
+r3          Volatile      (Parameter 1, and return value.)
+r4-r8       Volatile      (Parameters 2-6.)
 =========== ============= ========================================
 
 All floating point and vector data registers as well as control and status
 registers are nonvolatile.
 
-Invocation
-----------
-The syscall is performed with the sc instruction, and returns with execution
-continuing at the instruction following the sc instruction.
-
 Transactional Memory
 --------------------
 Syscall behavior can change if the processor is in transactional or suspended
@@ -75,6 +92,7 @@ auxiliary vector.
   returning to the caller. This case is not well defined or supported, so this
   behavior should not be relied upon.
 
+scv 0 syscalls will always behave as PPC_FEATURE2_HTM_NOSC.
 
 vsyscall
 ========

arch/powerpc/include/asm/asm-prototypes.h

@@ -98,7 +98,7 @@ unsigned long __init early_init(unsigned long dt_ptr);
 void __init machine_init(u64 dt_ptr);
 #endif
 long system_call_exception(long r3, long r4, long r5, long r6, long r7, long r8, unsigned long r0, struct pt_regs *regs);
-notrace unsigned long syscall_exit_prepare(unsigned long r3, struct pt_regs *regs);
+notrace unsigned long syscall_exit_prepare(unsigned long r3, struct pt_regs *regs, long scv);
 notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned long msr);
 notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsigned long msr);
 

arch/powerpc/include/asm/exception-64s.h

@@ -131,6 +131,12 @@
 	hrfid;								\
 	b	hrfi_flush_fallback
 
+#define RFSCV_TO_USER							\
+	STF_EXIT_BARRIER_SLOT;						\
+	RFI_FLUSH_SLOT;							\
+	RFSCV;								\
+	b	rfscv_flush_fallback
+
 #endif /* __ASSEMBLY__ */
 
 #endif	/* _ASM_POWERPC_EXCEPTION_H */

arch/powerpc/include/asm/head-64.h

@@ -128,7 +128,7 @@ end_##sname:
 	.if ((start) % (size) != 0);				\
 	.error "Fixed section exception vector misalignment";	\
 	.endif;							\
-	.if ((size) != 0x20) && ((size) != 0x80) && ((size) != 0x100); \
+	.if ((size) != 0x20) && ((size) != 0x80) && ((size) != 0x100) && ((size) != 0x1000); \
 	.error "Fixed section exception vector bad size";	\
 	.endif;							\
 	.if (start) < sname##_start;				\

arch/powerpc/include/asm/ppc_asm.h

@@ -755,6 +755,8 @@ END_FTR_SECTION_NESTED(CPU_FTR_CELL_TB_BUG, CPU_FTR_CELL_TB_BUG, 96)
 #define N_SLINE	68
 #define N_SO	100
 
+#define RFSCV	.long 0x4c0000a4
+
 /*
  * Create an endian fixup trampoline
  *

arch/powerpc/include/asm/ptrace.h

@@ -222,9 +222,14 @@ static inline void set_trap(struct pt_regs *regs, unsigned long val)
 	regs->trap = (regs->trap & TRAP_FLAGS_MASK) | (val & ~TRAP_FLAGS_MASK);
 }
 
+static inline bool trap_is_scv(struct pt_regs *regs)
+{
+	return (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && TRAP(regs) == 0x3000);
+}
+
 static inline bool trap_is_syscall(struct pt_regs *regs)
 {
-	return TRAP(regs) == 0xc00;
+	return (trap_is_scv(regs) || TRAP(regs) == 0xc00);
 }
 
 static inline bool trap_norestart(struct pt_regs *regs)

arch/powerpc/include/asm/setup.h

@@ -30,12 +30,12 @@ void setup_panic(void);
 #define ARCH_PANIC_TIMEOUT 180
 
 #ifdef CONFIG_PPC_PSERIES
-extern void pseries_enable_reloc_on_exc(void);
+extern bool pseries_enable_reloc_on_exc(void);
 extern void pseries_disable_reloc_on_exc(void);
 extern void pseries_big_endian_exceptions(void);
 extern void pseries_little_endian_exceptions(void);
 #else
-static inline void pseries_enable_reloc_on_exc(void) {}
+static inline bool pseries_enable_reloc_on_exc(void) { return false; }
 static inline void pseries_disable_reloc_on_exc(void) {}
 static inline void pseries_big_endian_exceptions(void) {}
 static inline void pseries_little_endian_exceptions(void) {}

arch/powerpc/include/asm/sstep.h

@@ -40,6 +40,7 @@ enum instruction_type {
 	CACHEOP,
 	BARRIER,
 	SYSCALL,
+	SYSCALL_VECTORED_0,
 	MFMSR,
 	MTMSR,
 	RFI,

arch/powerpc/kernel/cpu_setup_power.S

@@ -98,7 +98,7 @@ _GLOBAL(__setup_cpu_power10)
 
 _GLOBAL(__setup_cpu_power9)
 	mflr	r11
-	bl	__init_FSCR
+	bl	__init_FSCR_power9
 1:	bl	__init_PMU
 	bl	__init_hvmode_206
 	mtlr	r11
@@ -128,7 +128,7 @@ _GLOBAL(__restore_cpu_power10)
 
 _GLOBAL(__restore_cpu_power9)
 	mflr	r11
-	bl	__init_FSCR
+	bl	__init_FSCR_power9
 1:	bl	__init_PMU
 	mfmsr	r3
 	rldicl.	r0,r3,4,63
@@ -198,6 +198,12 @@ __init_FSCR_power10:
 	mtspr	SPRN_FSCR, r3
 	// fall through
 
+__init_FSCR_power9:
+	mfspr	r3, SPRN_FSCR
+	ori	r3, r3, FSCR_SCV
+	mtspr	SPRN_FSCR, r3
+	// fall through
+
 __init_FSCR:
 	mfspr	r3,SPRN_FSCR
 	ori	r3,r3,FSCR_TAR|FSCR_EBB

arch/powerpc/kernel/cputable.c

@@ -120,7 +120,8 @@ extern void __restore_cpu_e6500(void);
 #define COMMON_USER2_POWER9	(COMMON_USER2_POWER8 | \
 				 PPC_FEATURE2_ARCH_3_00 | \
 				 PPC_FEATURE2_HAS_IEEE128 | \
-				 PPC_FEATURE2_DARN )
+				 PPC_FEATURE2_DARN | \
+				 PPC_FEATURE2_SCV)
 #define COMMON_USER_POWER10	COMMON_USER_POWER9
 #define COMMON_USER2_POWER10	(COMMON_USER2_POWER9 | \
 				 PPC_FEATURE2_ARCH_3_1 | \

arch/powerpc/kernel/dt_cpu_ftrs.c

@@ -621,6 +621,7 @@ static struct dt_cpu_feature_match __initdata
 	{"little-endian", feat_enable_le, CPU_FTR_REAL_LE},
 	{"smt", feat_enable_smt, 0},
 	{"interrupt-facilities", feat_enable, 0},
+	{"system-call-vectored", feat_enable, 0},
 	{"timer-facilities", feat_enable, 0},
 	{"timer-facilities-v3", feat_enable, 0},
 	{"debug-facilities", feat_enable, 0},

arch/powerpc/kernel/entry_64.S

@@ -64,15 +64,173 @@ exception_marker:
 	.section	".text"
 	.align 7
 
+#ifdef CONFIG_PPC_BOOK3S
+.macro system_call_vectored name trapnr
+	.globl system_call_vectored_\name
+system_call_vectored_\name:
+_ASM_NOKPROBE_SYMBOL(system_call_vectored_\name)
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+BEGIN_FTR_SECTION
+	extrdi.	r10, r12, 1, (63-MSR_TS_T_LG) /* transaction active? */
+	bne	.Ltabort_syscall
+END_FTR_SECTION_IFSET(CPU_FTR_TM)
+#endif
+	INTERRUPT_TO_KERNEL
+	mr	r10,r1
+	ld	r1,PACAKSAVE(r13)
+	std	r10,0(r1)
+	std	r11,_NIP(r1)
+	std	r12,_MSR(r1)
+	std	r0,GPR0(r1)
+	std	r10,GPR1(r1)
+	std	r2,GPR2(r1)
+	ld	r2,PACATOC(r13)
+	mfcr	r12
+	li	r11,0
+	/* Can we avoid saving r3-r8 in common case? */
+	std	r3,GPR3(r1)
+	std	r4,GPR4(r1)
+	std	r5,GPR5(r1)
+	std	r6,GPR6(r1)
+	std	r7,GPR7(r1)
+	std	r8,GPR8(r1)
+	/* Zero r9-r12, this should only be required when restoring all GPRs */
+	std	r11,GPR9(r1)
+	std	r11,GPR10(r1)
+	std	r11,GPR11(r1)
+	std	r11,GPR12(r1)
+	std	r9,GPR13(r1)
+	SAVE_NVGPRS(r1)
+	std	r11,_XER(r1)
+	std	r11,_LINK(r1)
+	std	r11,_CTR(r1)
+
+	li	r11,\trapnr
+	std	r11,_TRAP(r1)
+	std	r12,_CCR(r1)
+	std	r3,ORIG_GPR3(r1)
+	addi	r10,r1,STACK_FRAME_OVERHEAD
+	ld	r11,exception_marker@toc(r2)
+	std	r11,-16(r10)		/* "regshere" marker */
+
+	/*
+	 * RECONCILE_IRQ_STATE without calling trace_hardirqs_off(), which
+	 * would clobber syscall parameters. Also we always enter with IRQs
+	 * enabled and nothing pending. system_call_exception() will call
+	 * trace_hardirqs_off().
+	 *
+	 * scv enters with MSR[EE]=1, so don't set PACA_IRQ_HARD_DIS. The
+	 * entry vector already sets PACAIRQSOFTMASK to IRQS_ALL_DISABLED.
+	 */
+
+	/* Calling convention has r9 = orig r0, r10 = regs */
+	mr	r9,r0
+	bl	system_call_exception
+
+.Lsyscall_vectored_\name\()_exit:
+	addi    r4,r1,STACK_FRAME_OVERHEAD
+	li	r5,1 /* scv */
+	bl	syscall_exit_prepare
+
+	ld	r2,_CCR(r1)
+	ld	r4,_NIP(r1)
+	ld	r5,_MSR(r1)
+
+BEGIN_FTR_SECTION
+	stdcx.	r0,0,r1			/* to clear the reservation */
+END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
+
+BEGIN_FTR_SECTION
+	HMT_MEDIUM_LOW
+END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
+
+	cmpdi	r3,0
+	bne	.Lsyscall_vectored_\name\()_restore_regs
+
+	/* rfscv returns with LR->NIA and CTR->MSR */
+	mtlr	r4
+	mtctr	r5
+
+	/* Could zero these as per ABI, but we may consider a stricter ABI
+	 * which preserves these if libc implementations can benefit, so
+	 * restore them for now until further measurement is done. */
+	ld	r0,GPR0(r1)
+	ld	r4,GPR4(r1)
+	ld	r5,GPR5(r1)
+	ld	r6,GPR6(r1)
+	ld	r7,GPR7(r1)
+	ld	r8,GPR8(r1)
+	/* Zero volatile regs that may contain sensitive kernel data */
+	li	r9,0
+	li	r10,0
+	li	r11,0
+	li	r12,0
+	mtspr	SPRN_XER,r0
+
+	/*
+	 * We don't need to restore AMR on the way back to userspace for KUAP.
+	 * The value of AMR only matters while we're in the kernel.
+	 */
+	mtcr	r2
+	ld	r2,GPR2(r1)
+	ld	r3,GPR3(r1)
+	ld	r13,GPR13(r1)
+	ld	r1,GPR1(r1)
+	RFSCV_TO_USER
+	b	.	/* prevent speculative execution */
+
+.Lsyscall_vectored_\name\()_restore_regs:
+	li	r3,0
+	mtmsrd	r3,1
+	mtspr	SPRN_SRR0,r4
+	mtspr	SPRN_SRR1,r5
+
+	ld	r3,_CTR(r1)
+	ld	r4,_LINK(r1)
+	ld	r5,_XER(r1)
+
+	REST_NVGPRS(r1)
+	ld	r0,GPR0(r1)
+	mtcr	r2
+	mtctr	r3
+	mtlr	r4
+	mtspr	SPRN_XER,r5
+	REST_10GPRS(2, r1)
+	REST_2GPRS(12, r1)
+	ld	r1,GPR1(r1)
+	RFI_TO_USER
+.endm
+
+system_call_vectored common 0x3000
+/*
+ * We instantiate another entry copy for the SIGILL variant, with TRAP=0x7ff0
+ * which is tested by system_call_exception when r0 is -1 (as set by vector
+ * entry code).
+ */
+system_call_vectored sigill 0x7ff0
+
+
+/*
+ * Entered via kernel return set up by kernel/sstep.c, must match entry regs
+ */
+	.globl system_call_vectored_emulate
+system_call_vectored_emulate:
+_ASM_NOKPROBE_SYMBOL(system_call_vectored_emulate)
+	li	r10,IRQS_ALL_DISABLED
+	stb	r10,PACAIRQSOFTMASK(r13)
+	b	system_call_vectored_common
+#endif
+
+	.balign IFETCH_ALIGN_BYTES
 	.globl system_call_common
 system_call_common:
+_ASM_NOKPROBE_SYMBOL(system_call_common)
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
 BEGIN_FTR_SECTION
 	extrdi.	r10, r12, 1, (63-MSR_TS_T_LG) /* transaction active? */
 	bne	.Ltabort_syscall
 END_FTR_SECTION_IFSET(CPU_FTR_TM)
 #endif
-_ASM_NOKPROBE_SYMBOL(system_call_common)
 	mr	r10,r1
 	ld	r1,PACAKSAVE(r13)
 	std	r10,0(r1)
@@ -138,6 +296,7 @@ END_BTB_FLUSH_SECTION
 
 .Lsyscall_exit:
 	addi    r4,r1,STACK_FRAME_OVERHEAD
+	li	r5,0 /* !scv */
 	bl	syscall_exit_prepare
 
 	ld	r2,_CCR(r1)
@@ -224,10 +383,18 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 	b	.	/* prevent speculative execution */
 #endif
 
+#ifdef CONFIG_PPC_BOOK3S
+_GLOBAL(ret_from_fork_scv)
+	bl	schedule_tail
+	REST_NVGPRS(r1)
+	li	r3,0	/* fork() return value */
+	b	.Lsyscall_vectored_common_exit
+#endif
+
 _GLOBAL(ret_from_fork)
 	bl	schedule_tail
 	REST_NVGPRS(r1)
-	li	r3,0
+	li	r3,0	/* fork() return value */
 	b	.Lsyscall_exit
 
 _GLOBAL(ret_from_kernel_thread)

arch/powerpc/kernel/exceptions-64s.S

@@ -508,8 +508,24 @@ DEFINE_FIXED_SYMBOL(\name\()_common_real)
 
 .macro __GEN_COMMON_BODY name
 	.if IMASK
+		.if ! ISTACK
+		.error "No support for masked interrupt to use custom stack"
+		.endif
+
+		/* If coming from user, skip soft-mask tests. */
+		andi.	r10,r12,MSR_PR
+		bne	2f
+
+		/* Kernel code running below __end_interrupts is implicitly
+		 * soft-masked */
+		LOAD_HANDLER(r10, __end_interrupts)
+		cmpld	r11,r10
+		li	r10,IMASK
+		blt-	1f
+
+		/* Test the soft mask state against our interrupt's bit */
 		lbz	r10,PACAIRQSOFTMASK(r13)
-		andi.	r10,r10,IMASK
+1:		andi.	r10,r10,IMASK
 		/* Associate vector numbers with bits in paca->irq_happened */
 		.if IVEC == 0x500 || IVEC == 0xea0
 		li	r10,PACA_IRQ_EE
@@ -540,7 +556,7 @@ DEFINE_FIXED_SYMBOL(\name\()_common_real)
 
 	.if ISTACK
 	andi.	r10,r12,MSR_PR		/* See if coming from user	*/
-	mr	r10,r1			/* Save r1			*/
+2:	mr	r10,r1			/* Save r1			*/
 	subi	r1,r1,INT_FRAME_SIZE	/* alloc frame on kernel stack	*/
 	beq-	100f
 	ld	r1,PACAKSAVE(r13)	/* kernel stack to use		*/
@@ -740,6 +756,9 @@ END_FTR_SECTION_IFSET(CPU_FTR_CAN_NAP)
  * guarantee they will be delivered virtually. Some conditions (see the ISA)
  * cause exceptions to be delivered in real mode.
  *
+ * The scv instructions are a special case. They get a 0x3000 offset applied.
+ * scv exceptions have unique reentrancy properties, see below.
+ *
  * It's impossible to receive interrupts below 0x300 via AIL.
  *
  * KVM: None of the virtual exceptions are from the guest. Anything that
@@ -749,8 +768,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_CAN_NAP)
  * We layout physical memory as follows:
  * 0x0000 - 0x00ff : Secondary processor spin code
  * 0x0100 - 0x18ff : Real mode pSeries interrupt vectors
- * 0x1900 - 0x3fff : Real mode trampolines
- * 0x4000 - 0x58ff : Relon (IR=1,DR=1) mode pSeries interrupt vectors
+ * 0x1900 - 0x2fff : Real mode trampolines
+ * 0x3000 - 0x58ff : Relon (IR=1,DR=1) mode pSeries interrupt vectors
  * 0x5900 - 0x6fff : Relon mode trampolines
  * 0x7000 - 0x7fff : FWNMI data area
  * 0x8000 -   .... : Common interrupt handlers, remaining early
@@ -761,8 +780,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_CAN_NAP)
  * vectors there.
  */
 OPEN_FIXED_SECTION(real_vectors,        0x0100, 0x1900)
-OPEN_FIXED_SECTION(real_trampolines,    0x1900, 0x4000)
-OPEN_FIXED_SECTION(virt_vectors,        0x4000, 0x5900)
+OPEN_FIXED_SECTION(real_trampolines,    0x1900, 0x3000)
+OPEN_FIXED_SECTION(virt_vectors,        0x3000, 0x5900)
 OPEN_FIXED_SECTION(virt_trampolines,    0x5900, 0x7000)
 
 #ifdef CONFIG_PPC_POWERNV
@@ -798,6 +817,77 @@ USE_FIXED_SECTION(real_vectors)
 	.globl __start_interrupts
 __start_interrupts:
 
+/**
+ * Interrupt 0x3000 - System Call Vectored Interrupt (syscall).
+ * This is a synchronous interrupt invoked with the "scv" instruction. The
+ * system call does not alter the HV bit, so it is directed to the OS.
+ *
+ * Handling:
+ * scv instructions enter the kernel without changing EE, RI, ME, or HV.
+ * In particular, this means we can take a maskable interrupt at any point
+ * in the scv handler, which is unlike any other interrupt. This is solved
+ * by treating the instruction addresses below __end_interrupts as being
+ * soft-masked.
+ *
+ * AIL-0 mode scv exceptions go to 0x17000-0x17fff, but we set AIL-3 and
+ * ensure scv is never executed with relocation off, which means AIL-0
+ * should never happen.
+ *
+ * Before leaving the below __end_interrupts text, at least of the following
+ * must be true:
+ * - MSR[PR]=1 (i.e., return to userspace)
+ * - MSR_EE|MSR_RI is set (no reentrant exceptions)
+ * - Standard kernel environment is set up (stack, paca, etc)
+ *
+ * Call convention:
+ *
+ * syscall register convention is in Documentation/powerpc/syscall64-abi.rst
+ */
+EXC_VIRT_BEGIN(system_call_vectored, 0x3000, 0x1000)
+	/* SCV 0 */
+	mr	r9,r13
+	GET_PACA(r13)
+	mflr	r11
+	mfctr	r12
+	li	r10,IRQS_ALL_DISABLED
+	stb	r10,PACAIRQSOFTMASK(r13)
+#ifdef CONFIG_RELOCATABLE
+	b	system_call_vectored_tramp
+#else
+	b	system_call_vectored_common
+#endif
+	nop
+
+	/* SCV 1 - 127 */
+	.rept	127
+	mr	r9,r13
+	GET_PACA(r13)
+	mflr	r11
+	mfctr	r12
+	li	r10,IRQS_ALL_DISABLED
+	stb	r10,PACAIRQSOFTMASK(r13)
+	li	r0,-1 /* cause failure */
+#ifdef CONFIG_RELOCATABLE
+	b	system_call_vectored_sigill_tramp
+#else
+	b	system_call_vectored_sigill
+#endif
+	.endr
+EXC_VIRT_END(system_call_vectored, 0x3000, 0x1000)
+
+#ifdef CONFIG_RELOCATABLE
+TRAMP_VIRT_BEGIN(system_call_vectored_tramp)
+	__LOAD_HANDLER(r10, system_call_vectored_common)
+	mtctr	r10
+	bctr
+
+TRAMP_VIRT_BEGIN(system_call_vectored_sigill_tramp)
+	__LOAD_HANDLER(r10, system_call_vectored_sigill)
+	mtctr	r10
+	bctr
+#endif
+
+
 /* No virt vectors corresponding with 0x0..0x100 */
 EXC_VIRT_NONE(0x4000, 0x100)
 
@@ -2838,7 +2928,8 @@ masked_interrupt:
 	ld	r10,PACA_EXGEN+EX_R10(r13)
 	ld	r11,PACA_EXGEN+EX_R11(r13)
 	ld	r12,PACA_EXGEN+EX_R12(r13)
-	/* returns to kernel where r13 must be set up, so don't restore it */
+	ld	r13,PACA_EXGEN+EX_R13(r13)
+	/* May return to masked low address where r13 is not set up */
 	.if \hsrr
 	HRFI_TO_KERNEL
 	.else
@@ -2946,6 +3037,47 @@ TRAMP_REAL_BEGIN(hrfi_flush_fallback)
 	GET_SCRATCH0(r13);
 	hrfid
 
+TRAMP_REAL_BEGIN(rfscv_flush_fallback)
+	/* system call volatile */
+	mr	r7,r13
+	GET_PACA(r13);
+	mr	r8,r1
+	ld	r1,PACAKSAVE(r13)
+	mfctr	r9
+	ld	r10,PACA_RFI_FLUSH_FALLBACK_AREA(r13)
+	ld	r11,PACA_L1D_FLUSH_SIZE(r13)
+	srdi	r11,r11,(7 + 3) /* 128 byte lines, unrolled 8x */
+	mtctr	r11
+	DCBT_BOOK3S_STOP_ALL_STREAM_IDS(r11) /* Stop prefetch streams */
+
+	/* order ld/st prior to dcbt stop all streams with flushing */
+	sync
+
+	/*
+	 * The load adresses are at staggered offsets within cachelines,
+	 * which suits some pipelines better (on others it should not
+	 * hurt).
+	 */
+1:
+	ld	r11,(0x80 + 8)*0(r10)
+	ld	r11,(0x80 + 8)*1(r10)
+	ld	r11,(0x80 + 8)*2(r10)
+	ld	r11,(0x80 + 8)*3(r10)
+	ld	r11,(0x80 + 8)*4(r10)
+	ld	r11,(0x80 + 8)*5(r10)
+	ld	r11,(0x80 + 8)*6(r10)
+	ld	r11,(0x80 + 8)*7(r10)
+	addi	r10,r10,0x80*8
+	bdnz	1b
+
+	mtctr	r9
+	li	r9,0
+	li	r10,0
+	li	r11,0
+	mr	r1,r8
+	mr	r13,r7
+	RFSCV
+
 USE_TEXT_SECTION()
 	MASKED_INTERRUPT
 	MASKED_INTERRUPT hsrr=1
@@ -2997,6 +3129,10 @@ EXC_COMMON_BEGIN(ppc64_runlatch_on_trampoline)
 
 USE_FIXED_SECTION(virt_trampolines)
 	/*
+	 * All code below __end_interrupts is treated as soft-masked. If
+	 * any code runs here with MSR[EE]=1, it must then cope with pending
+	 * soft interrupt being raised (i.e., by ensuring it is replayed).
+	 *
 	 * The __end_interrupts marker must be past the out-of-line (OOL)
 	 * handlers, so that they are copied to real address 0x100 when running
 	 * a relocatable kernel. This ensures they can be reached from the short

arch/powerpc/kernel/process.c

@@ -1618,6 +1618,7 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
 {
 	struct pt_regs *childregs, *kregs;
 	extern void ret_from_fork(void);
+	extern void ret_from_fork_scv(void);
 	extern void ret_from_kernel_thread(void);
 	void (*f)(void);
 	unsigned long sp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
@@ -1654,6 +1655,8 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
 		if (usp)
 			childregs->gpr[1] = usp;
 		p->thread.regs = childregs;
+		/* 64s sets this in ret_from_fork */
+		if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64))
 			childregs->gpr[3] = 0;  /* Result from fork() */
 		if (clone_flags & CLONE_SETTLS) {
 			if (!is_32bit_task())
@@ -1662,6 +1665,9 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
 				childregs->gpr[2] = tls;
 		}
 
+		if (trap_is_scv(regs))
+			f = ret_from_fork_scv;
+		else
 			f = ret_from_fork;
 	}
 	childregs->msr &= ~(MSR_FP|MSR_VEC|MSR_VSX);

arch/powerpc/kernel/setup_64.c

@@ -196,7 +196,10 @@ static void __init configure_exceptions(void)
 	/* Under a PAPR hypervisor, we need hypercalls */
 	if (firmware_has_feature(FW_FEATURE_SET_MODE)) {
 		/* Enable AIL if possible */
-		pseries_enable_reloc_on_exc();
+		if (!pseries_enable_reloc_on_exc()) {
+			init_task.thread.fscr &= ~FSCR_SCV;
+			cur_cpu_spec->cpu_user_features2 &= ~PPC_FEATURE2_SCV;
+		}
 
 		/*
 		 * Tell the hypervisor that we want our exceptions to

arch/powerpc/kernel/signal.c

@@ -205,8 +205,14 @@ static void check_syscall_restart(struct pt_regs *regs, struct k_sigaction *ka,
 		return;
 
 	/* error signalled ? */
-	if (!(regs->ccr & 0x10000000))
+	if (trap_is_scv(regs)) {
+		/* 32-bit compat mode sign extend? */
+		if (!IS_ERR_VALUE(ret))
 			return;
+		ret = -ret;
+	} else if (!(regs->ccr & 0x10000000)) {
+		return;
+	}
 
 	switch (ret) {
 	case ERESTART_RESTARTBLOCK:
@@ -238,11 +244,16 @@ static void check_syscall_restart(struct pt_regs *regs, struct k_sigaction *ka,
 			regs->gpr[3] = regs->orig_gpr3;
 		regs->nip -= 4;
 		regs->result = 0;
+	} else {
+		if (trap_is_scv(regs)) {
+			regs->result = -EINTR;
+			regs->gpr[3] = -EINTR;
 		} else {
 			regs->result = -EINTR;
 			regs->gpr[3] = EINTR;
 			regs->ccr |= 0x10000000;
 		}
+	}
 }
 
 static void do_signal(struct task_struct *tsk)

arch/powerpc/kernel/syscall_64.c

@@ -60,6 +60,11 @@ notrace long system_call_exception(long r3, long r4, long r5,
 	local_irq_enable();
 
 	if (unlikely(current_thread_info()->flags & _TIF_SYSCALL_DOTRACE)) {
+		if (unlikely(regs->trap == 0x7ff0)) {
+			/* Unsupported scv vector */
+			_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
+			return regs->gpr[3];
+		}
 		/*
 		 * We use the return value of do_syscall_trace_enter() as the
 		 * syscall number. If the syscall was rejected for any reason
@@ -78,6 +83,11 @@ notrace long system_call_exception(long r3, long r4, long r5,
 		r8 = regs->gpr[8];
 
 	} else if (unlikely(r0 >= NR_syscalls)) {
+		if (unlikely(regs->trap == 0x7ff0)) {
+			/* Unsupported scv vector */
+			_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
+			return regs->gpr[3];
+		}
 		return -ENOSYS;
 	}
 
@@ -105,15 +115,19 @@ notrace long system_call_exception(long r3, long r4, long r5,
  * local irqs must be disabled. Returns false if the caller must re-enable
  * them, check for new work, and try again.
  */
-static notrace inline bool prep_irq_for_enabled_exit(void)
+static notrace inline bool prep_irq_for_enabled_exit(bool clear_ri)
 {
 	/* This must be done with RI=1 because tracing may touch vmaps */
 	trace_hardirqs_on();
 
 	/* This pattern matches prep_irq_for_idle */
+	if (clear_ri)
 		__hard_EE_RI_disable();
+	else
+		__hard_irq_disable();
 	if (unlikely(lazy_irq_pending_nocheck())) {
 		/* Took an interrupt, may have more exit work to do. */
+		if (clear_ri)
 			__hard_RI_enable();
 		trace_hardirqs_off();
 		local_paca->irq_happened |= PACA_IRQ_HARD_DIS;
@@ -136,7 +150,8 @@ static notrace inline bool prep_irq_for_enabled_exit(void)
  * because RI=0 and soft mask state is "unreconciled", so it is marked notrace.
  */
 notrace unsigned long syscall_exit_prepare(unsigned long r3,
-					   struct pt_regs *regs)
+					   struct pt_regs *regs,
+					   long scv)
 {
 	unsigned long *ti_flagsp = &current_thread_info()->flags;
 	unsigned long ti_flags;
@@ -151,7 +166,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 
 	ti_flags = *ti_flagsp;
 
-	if (unlikely(r3 >= (unsigned long)-MAX_ERRNO)) {
+	if (unlikely(r3 >= (unsigned long)-MAX_ERRNO) && !scv) {
 		if (likely(!(ti_flags & (_TIF_NOERROR | _TIF_RESTOREALL)))) {
 			r3 = -r3;
 			regs->ccr |= 0x10000000; /* Set SO bit in CR */
@@ -218,7 +233,8 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 		}
 	}
 
-	if (unlikely(!prep_irq_for_enabled_exit())) {
+	/* scv need not set RI=0 because SRRs are not used */
+	if (unlikely(!prep_irq_for_enabled_exit(!scv))) {
 		local_irq_enable();
 		goto again;
 	}
@@ -290,7 +306,7 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned
 		}
 	}
 
-	if (unlikely(!prep_irq_for_enabled_exit())) {
+	if (unlikely(!prep_irq_for_enabled_exit(true))) {
 		local_irq_enable();
 		local_irq_disable();
 		goto again;
@@ -353,7 +369,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsign
 			}
 		}
 
-		if (unlikely(!prep_irq_for_enabled_exit())) {
+		if (unlikely(!prep_irq_for_enabled_exit(true))) {
 			/*
 			 * Can't local_irq_restore to replay if we were in
 			 * interrupt context. Must replay directly.

arch/powerpc/lib/sstep.c

@@ -16,6 +16,7 @@
 #include <asm/disassemble.h>
 
 extern char system_call_common[];
+extern char system_call_vectored_emulate[];
 
 #ifdef CONFIG_PPC64
 /* Bits in SRR1 that are copied from MSR */
@@ -1236,6 +1237,9 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 	case 17:	/* sc */
 		if ((word & 0xfe2) == 2)
 			op->type = SYSCALL;
+		else if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) &&
+				(word & 0xfe3) == 1)
+			op->type = SYSCALL_VECTORED_0;
 		else
 			op->type = UNKNOWN;
 		return 0;
@@ -3378,6 +3382,18 @@ int emulate_step(struct pt_regs *regs, struct ppc_inst instr)
 		regs->msr = MSR_KERNEL;
 		return 1;
 
+#ifdef CONFIG_PPC64_BOOK3S
+	case SYSCALL_VECTORED_0:	/* scv 0 */
+		regs->gpr[9] = regs->gpr[13];
+		regs->gpr[10] = MSR_KERNEL;
+		regs->gpr[11] = regs->nip + 4;
+		regs->gpr[12] = regs->msr & MSR_MASK;
+		regs->gpr[13] = (unsigned long) get_paca();
+		regs->nip = (unsigned long) &system_call_vectored_emulate;
+		regs->msr = MSR_KERNEL;
+		return 1;
+#endif
+
 	case RFI:
 		return -1;
 #endif

arch/powerpc/platforms/pseries/setup.c

@@ -358,7 +358,7 @@ static void pseries_lpar_idle(void)
  * to ever be a problem in practice we can move this into a kernel thread to
  * finish off the process later in boot.
  */
-void pseries_enable_reloc_on_exc(void)
+bool pseries_enable_reloc_on_exc(void)
 {
 	long rc;
 	unsigned int delay, total_delay = 0;
@@ -369,11 +369,13 @@ void pseries_enable_reloc_on_exc(void)
 			if (rc == H_P2) {
 				pr_info("Relocation on exceptions not"
 					" supported\n");
+				return false;
 			} else if (rc != H_SUCCESS) {
 				pr_warn("Unable to enable relocation"
 					" on exceptions: %ld\n", rc);
+				return false;
 			}
-			break;
+			return true;
 		}
 
 		delay = get_longbusy_msecs(rc);
@@ -382,7 +384,7 @@ void pseries_enable_reloc_on_exc(void)
 			pr_warn("Warning: Giving up waiting to enable "
 				"relocation on exceptions (%u msec)!\n",
 				total_delay);
-			return;
+			return false;
 		}
 
 		mdelay(delay);

arch/powerpc/xmon/xmon.c

@@ -1600,6 +1600,7 @@ const char *getvecname(unsigned long vec)
 	case 0x1300:	ret = "(Instruction Breakpoint)"; break;
 	case 0x1500:	ret = "(Denormalisation)"; break;
 	case 0x1700:	ret = "(Altivec Assist)"; break;
+	case 0x3000:	ret = "(System Call Vectored)"; break;
 	default: ret = "";
 	}
 	return ret;