s390/fpu: convert FPU CIF flag to regular TIF flag

The FPU state, as represented by the CIF_FPU flag reflects the FPU state of
a task, not the CPU it is running on. Therefore convert the flag to a
regular TIF flag.

This removes the magic in switch_to() where a save_fpu_regs() call for the
currently (previous) running task sets the per-cpu CIF_FPU flag, which is
required to restore FPU register contents of the next task, when it returns
to user space.
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/include/asm/entry-common.h

@@ -41,7 +41,7 @@ static __always_inline void arch_exit_to_user_mode_work(struct pt_regs *regs,
 
 static __always_inline void arch_exit_to_user_mode(void)
 {
-	if (test_cpu_flag(CIF_FPU))
+	if (test_thread_flag(TIF_FPU))
 		__load_fpu_regs();
 
 	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))

arch/s390/include/asm/fpu.h

@@ -148,7 +148,7 @@ static inline void kernel_fpu_begin(struct kernel_fpu *state, u32 flags)
 {
 	preempt_disable();
 	state->mask = S390_lowcore.fpu_flags;
-	if (!test_cpu_flag(CIF_FPU)) {
+	if (!test_thread_flag(TIF_FPU)) {
 		/* Save user space FPU state and register contents */
 		save_fpu_regs();
 	} else if (state->mask & flags) {

arch/s390/include/asm/processor.h

@@ -15,13 +15,11 @@
 #include <linux/bits.h>
 
 #define CIF_NOHZ_DELAY		2	/* delay HZ disable for a tick */
-#define CIF_FPU			3	/* restore FPU registers */
 #define CIF_ENABLED_WAIT	5	/* in enabled wait state */
 #define CIF_MCCK_GUEST		6	/* machine check happening in guest */
 #define CIF_DEDICATED_CPU	7	/* this CPU is dedicated */
 
 #define _CIF_NOHZ_DELAY		BIT(CIF_NOHZ_DELAY)
-#define _CIF_FPU		BIT(CIF_FPU)
 #define _CIF_ENABLED_WAIT	BIT(CIF_ENABLED_WAIT)
 #define _CIF_MCCK_GUEST		BIT(CIF_MCCK_GUEST)
 #define _CIF_DEDICATED_CPU	BIT(CIF_DEDICATED_CPU)

arch/s390/include/asm/thread_info.h

@@ -69,6 +69,7 @@ void arch_setup_new_exec(void);
 #define TIF_PATCH_PENDING	5	/* pending live patching update */
 #define TIF_PGSTE		6	/* New mm's will use 4K page tables */
 #define TIF_NOTIFY_SIGNAL	7	/* signal notifications exist */
+#define TIF_FPU			8	/* restore FPU registers on exit to usermode */
 #define TIF_ISOLATE_BP_GUEST	9	/* Run KVM guests with isolated BP */
 #define TIF_PER_TRAP		10	/* Need to handle PER trap on exit to usermode */
 
@@ -92,6 +93,7 @@ void arch_setup_new_exec(void);
 #define _TIF_UPROBE		BIT(TIF_UPROBE)
 #define _TIF_GUARDED_STORAGE	BIT(TIF_GUARDED_STORAGE)
 #define _TIF_PATCH_PENDING	BIT(TIF_PATCH_PENDING)
+#define _TIF_FPU		BIT(TIF_FPU)
 #define _TIF_ISOLATE_BP_GUEST	BIT(TIF_ISOLATE_BP_GUEST)
 #define _TIF_PER_TRAP		BIT(TIF_PER_TRAP)
 

arch/s390/kernel/entry.S

@@ -220,7 +220,7 @@ SYM_FUNC_START(__sie64a)
 	oi	__SIE_PROG0C+3(%r14),1		# we are going into SIE now
 	tm	__SIE_PROG20+3(%r14),3		# last exit...
 	jnz	.Lsie_skip
-	TSTMSK	__LC_CPU_FLAGS,_CIF_FPU
+	TSTMSK	__SF_SIE_FLAGS(%r15),_TIF_FPU
 	jo	.Lsie_skip			# exit if fp/vx regs changed
 	lg	%r14,__SF_SIE_CONTROL_PHYS(%r15)	# get sie block phys addr
 	BPEXIT	__SF_SIE_FLAGS(%r15),_TIF_ISOLATE_BP_GUEST

arch/s390/kernel/fpu.c

@@ -117,7 +117,7 @@ void __load_fpu_regs(void)
 		load_vx_regs(regs);
 	else
 		load_fp_regs(regs);
-	clear_cpu_flag(CIF_FPU);
+	clear_thread_flag(TIF_FPU);
 }
 
 void load_fpu_regs(void)
@@ -136,7 +136,7 @@ void save_fpu_regs(void)
 
 	local_irq_save(flags);
 
-	if (test_cpu_flag(CIF_FPU))
+	if (test_thread_flag(TIF_FPU))
 		goto out;
 
 	state = &current->thread.fpu;
@@ -147,7 +147,7 @@ void save_fpu_regs(void)
 		save_vx_regs(regs);
 	else
 		save_fp_regs(regs);
-	set_cpu_flag(CIF_FPU);
+	set_thread_flag(TIF_FPU);
 out:
 	local_irq_restore(flags);
 }

arch/s390/kernel/process.c

@@ -88,7 +88,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 {
 	/*
 	 * Save the floating-point or vector register state of the current
-	 * task and set the CIF_FPU flag to lazy restore the FPU register
+	 * task and set the TIF_FPU flag to lazy restore the FPU register
 	 * state when returning to user space.
 	 */
 	save_fpu_regs();
@@ -196,11 +196,6 @@ void execve_tail(void)
 
 struct task_struct *__switch_to(struct task_struct *prev, struct task_struct *next)
 {
-	/*
-	 * save_fpu_regs() sets the CIF_FPU flag, which enforces
-	 * a restore of the floating point / vector registers as
-	 * soon as the next task returns to user space.
-	 */
 	save_fpu_regs();
 	save_access_regs(&prev->thread.acrs[0]);
 	save_ri_cb(prev->thread.ri_cb);

arch/s390/kvm/kvm-s390.c

@@ -4829,7 +4829,7 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 			       vcpu->run->s.regs.gprs,
 			       sizeof(sie_page->pv_grregs));
 		}
-		if (test_cpu_flag(CIF_FPU))
+		if (test_thread_flag(TIF_FPU))
 			load_fpu_regs();
 		exit_reason = sie64a(vcpu->arch.sie_block,
 				     vcpu->run->s.regs.gprs);

arch/s390/kvm/vsie.c

@@ -1149,7 +1149,7 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 	 */
 	vcpu->arch.sie_block->prog0c |= PROG_IN_SIE;
 	barrier();
-	if (test_cpu_flag(CIF_FPU))
+	if (test_thread_flag(TIF_FPU))
 		load_fpu_regs();
 	if (!kvm_s390_vcpu_sie_inhibited(vcpu))
 		rc = sie64a(scb_s, vcpu->run->s.regs.gprs);