arm64: mm: Logic to make offset_ttbr1 conditional

When running with a 52-bit userspace VA and a 48-bit kernel VA we offset
ttbr1_el1 to allow the kernel pagetables with a 52-bit PTRS_PER_PGD to
be used for both userspace and kernel.

Moving on to a 52-bit kernel VA we no longer require this offset to
ttbr1_el1 should we be running on a system with HW support for 52-bit
VAs.

This patch introduces conditional logic to offset_ttbr1 to query
SYS_ID_AA64MMFR2_EL1 whenever 52-bit VAs are selected. If there is HW
support for 52-bit VAs then the ttbr1 offset is skipped.

We choose to read a system register rather than vabits_actual because
offset_ttbr1 can be called in places where the kernel data is not
actually mapped.

Calls to offset_ttbr1 appear to be made from rarely called code paths so
this extra logic is not expected to adversely affect performance.
Signed-off-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/assembler.h

@@ -538,9 +538,17 @@ USER(\label, ic	ivau, \tmp2)			// invalidate I line PoU
  * In future this may be nop'ed out when dealing with 52-bit kernel VAs.
  * 	ttbr: Value of ttbr to set, modified.
  */
-	.macro	offset_ttbr1, ttbr
+	.macro	offset_ttbr1, ttbr, tmp
 #ifdef CONFIG_ARM64_USER_VA_BITS_52
 	orr	\ttbr, \ttbr, #TTBR1_BADDR_4852_OFFSET
+#endif
+
+#ifdef CONFIG_ARM64_VA_BITS_52
+	mrs_s	\tmp, SYS_ID_AA64MMFR2_EL1
+	and	\tmp, \tmp, #(0xf << ID_AA64MMFR2_LVA_SHIFT)
+	cbnz	\tmp, .Lskipoffs_\@
+	orr	\ttbr, \ttbr, #TTBR1_BADDR_4852_OFFSET
+.Lskipoffs_\@ :
 #endif
 	.endm
 
@@ -550,7 +558,7 @@ USER(\label, ic	ivau, \tmp2)			// invalidate I line PoU
  * to be nop'ed out when dealing with 52-bit kernel VAs.
  */
 	.macro	restore_ttbr1, ttbr
-#ifdef CONFIG_ARM64_USER_VA_BITS_52
+#if defined(CONFIG_ARM64_USER_VA_BITS_52) || defined(CONFIG_ARM64_VA_BITS_52)
 	bic	\ttbr, \ttbr, #TTBR1_BADDR_4852_OFFSET
 #endif
 	.endm

arch/arm64/kernel/head.S

@@ -777,7 +777,7 @@ ENTRY(__enable_mmu)
 	phys_to_ttbr x1, x1
 	phys_to_ttbr x2, x2
 	msr	ttbr0_el1, x2			// load TTBR0
-	offset_ttbr1 x1
+	offset_ttbr1 x1, x3
 	msr	ttbr1_el1, x1			// load TTBR1
 	isb
 	msr	sctlr_el1, x0

arch/arm64/kernel/hibernate-asm.S

@@ -22,14 +22,14 @@
  * Even switching to our copied tables will cause a changed output address at
  * each stage of the walk.
  */
-.macro break_before_make_ttbr_switch zero_page, page_table, tmp
+.macro break_before_make_ttbr_switch zero_page, page_table, tmp, tmp2
 	phys_to_ttbr \tmp, \zero_page
 	msr	ttbr1_el1, \tmp
 	isb
 	tlbi	vmalle1
 	dsb	nsh
 	phys_to_ttbr \tmp, \page_table
-	offset_ttbr1 \tmp
+	offset_ttbr1 \tmp, \tmp2
 	msr	ttbr1_el1, \tmp
 	isb
 .endm
@@ -70,7 +70,7 @@ ENTRY(swsusp_arch_suspend_exit)
 	 * We execute from ttbr0, change ttbr1 to our copied linear map tables
 	 * with a break-before-make via the zero page
 	 */
-	break_before_make_ttbr_switch	x5, x0, x6
+	break_before_make_ttbr_switch	x5, x0, x6, x8
 
 	mov	x21, x1
 	mov	x30, x2
@@ -101,7 +101,7 @@ ENTRY(swsusp_arch_suspend_exit)
 	dsb	ish		/* wait for PoU cleaning to finish */
 
 	/* switch to the restored kernels page tables */
-	break_before_make_ttbr_switch	x25, x21, x6
+	break_before_make_ttbr_switch	x25, x21, x6, x8
 
 	ic	ialluis
 	dsb	ish

arch/arm64/mm/proc.S

@@ -168,7 +168,7 @@ ENDPROC(cpu_do_switch_mm)
 .macro	__idmap_cpu_set_reserved_ttbr1, tmp1, tmp2
 	adrp	\tmp1, empty_zero_page
 	phys_to_ttbr \tmp2, \tmp1
-	offset_ttbr1 \tmp2
+	offset_ttbr1 \tmp2, \tmp1
 	msr	ttbr1_el1, \tmp2
 	isb
 	tlbi	vmalle1
@@ -187,7 +187,7 @@ ENTRY(idmap_cpu_replace_ttbr1)
 
 	__idmap_cpu_set_reserved_ttbr1 x1, x3
 
-	offset_ttbr1 x0
+	offset_ttbr1 x0, x3
 	msr	ttbr1_el1, x0
 	isb
 
@@ -362,7 +362,7 @@ __idmap_kpti_secondary:
 	cbnz	w18, 1b
 
 	/* All done, act like nothing happened */
-	offset_ttbr1 swapper_ttb
+	offset_ttbr1 swapper_ttb, x18
 	msr	ttbr1_el1, swapper_ttb
 	isb
 	ret