arm64: mm: convert cpu_do_switch_mm() to C

There's no reason that cpu_do_switch_mm() needs to be written as an
assembly function, and having it as a C function would make it easier to
maintain.

This patch converts cpu_do_switch_mm() to C, removing code that this
change makes redundant (e.g. the mmid macro). Since the header comment
was stale and the prototype now implies all the necessary information,
this comment is removed. The 'pgd_phys' argument is made a phys_addr_t
to match the return type of virt_to_phys().

At the same time, post_ttbr_update_workaround() is updated to use
IS_ENABLED(), which allows the compiler to figure out it can elide calls
for !CONFIG_CAVIUM_ERRATUM_27456 builds.

There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
[catalin.marinas@arm.com: change comments from asm-style to C-style]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/assembler.h

@@ -256,12 +256,6 @@ alternative_endif
 	ldr	\rd, [\rn, #VMA_VM_MM]
 	.endm
 
-/*
- * mmid - get context id from mm pointer (mm->context.id)
- */
-	.macro	mmid, rd, rn
-	ldr	\rd, [\rn, #MM_CONTEXT_ID]
-	.endm
 /*
  * read_ctr - read CTR_EL0. If the system has mismatched register fields,
  * provide the system wide safe value from arm64_ftr_reg_ctrel0.sys_val

arch/arm64/include/asm/mmu_context.h

@@ -46,6 +46,8 @@ static inline void cpu_set_reserved_ttbr0(void)
 	isb();
 }
 
+void cpu_do_switch_mm(phys_addr_t pgd_phys, struct mm_struct *mm);
+
 static inline void cpu_switch_mm(pgd_t *pgd, struct mm_struct *mm)
 {
 	BUG_ON(pgd == swapper_pg_dir);

arch/arm64/include/asm/proc-fns.h

@@ -13,11 +13,9 @@
 
 #include <asm/page.h>
 
-struct mm_struct;
 struct cpu_suspend_ctx;
 
 extern void cpu_do_idle(void);
-extern void cpu_do_switch_mm(unsigned long pgd_phys, struct mm_struct *mm);
 extern void cpu_do_suspend(struct cpu_suspend_ctx *ptr);
 extern u64 cpu_do_resume(phys_addr_t ptr, u64 idmap_ttbr);
 

arch/arm64/mm/context.c

@@ -6,6 +6,7 @@
  * Copyright (C) 2012 ARM Ltd.
  */
 
+#include <linux/bitfield.h>
 #include <linux/bitops.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
@@ -254,10 +255,37 @@ void check_and_switch_context(struct mm_struct *mm, unsigned int cpu)
 /* Errata workaround post TTBRx_EL1 update. */
 asmlinkage void post_ttbr_update_workaround(void)
 {
+	if (!IS_ENABLED(CONFIG_CAVIUM_ERRATUM_27456))
+		return;
+
 	asm(ALTERNATIVE("nop; nop; nop",
 			"ic iallu; dsb nsh; isb",
-			ARM64_WORKAROUND_CAVIUM_27456,
-			CONFIG_CAVIUM_ERRATUM_27456));
+			ARM64_WORKAROUND_CAVIUM_27456));
+}
+
+void cpu_do_switch_mm(phys_addr_t pgd_phys, struct mm_struct *mm)
+{
+	unsigned long ttbr1 = read_sysreg(ttbr1_el1);
+	unsigned long asid = ASID(mm);
+	unsigned long ttbr0 = phys_to_ttbr(pgd_phys);
+
+	/* Skip CNP for the reserved ASID */
+	if (system_supports_cnp() && asid)
+		ttbr0 |= TTBR_CNP_BIT;
+
+	/* SW PAN needs a copy of the ASID in TTBR0 for entry */
+	if (IS_ENABLED(CONFIG_ARM64_SW_TTBR0_PAN))
+		ttbr0 |= FIELD_PREP(TTBR_ASID_MASK, asid);
+
+	/* Set ASID in TTBR1 since TCR.A1 is set */
+	ttbr1 &= ~TTBR_ASID_MASK;
+	ttbr1 |= FIELD_PREP(TTBR_ASID_MASK, asid);
+
+	write_sysreg(ttbr1, ttbr1_el1);
+	isb();
+	write_sysreg(ttbr0, ttbr0_el1);
+	isb();
+	post_ttbr_update_workaround();
 }
 
 static int asids_init(void)

arch/arm64/mm/proc.S

@@ -142,34 +142,6 @@ SYM_FUNC_END(cpu_do_resume)
 	.popsection
 #endif
 
-/*
- *	cpu_do_switch_mm(pgd_phys, tsk)
- *
- *	Set the translation table base pointer to be pgd_phys.
- *
- *	- pgd_phys - physical address of new TTB
- */
-SYM_FUNC_START(cpu_do_switch_mm)
-	mrs	x2, ttbr1_el1
-	mmid	x1, x1				// get mm->context.id
-	phys_to_ttbr x3, x0
-
-alternative_if ARM64_HAS_CNP
-	cbz     x1, 1f                          // skip CNP for reserved ASID
-	orr     x3, x3, #TTBR_CNP_BIT
-1:
-alternative_else_nop_endif
-#ifdef CONFIG_ARM64_SW_TTBR0_PAN
-	bfi	x3, x1, #48, #16		// set the ASID field in TTBR0
-#endif
-	bfi	x2, x1, #48, #16		// set the ASID
-	msr	ttbr1_el1, x2			// in TTBR1 (since TCR.A1 is set)
-	isb
-	msr	ttbr0_el1, x3			// now update TTBR0
-	isb
-	b	post_ttbr_update_workaround	// Back to C code...
-SYM_FUNC_END(cpu_do_switch_mm)
-
 	.pushsection ".idmap.text", "awx"
 
 .macro	__idmap_cpu_set_reserved_ttbr1, tmp1, tmp2