arm64: kexec: keep MMU enabled during kexec relocation

Now, that we have linear map page tables configured, keep MMU enabled
to allow faster relocation of segments to final destination.

Cavium ThunderX2:
Kernel Image size: 38M Iniramfs size: 46M Total relocation size: 84M
MMU-disabled:
relocation	7.489539915s
MMU-enabled:
relocation	0.03946095s

Broadcom Stingray:
The performance data: for a moderate size kernel + initramfs: 25M the
relocation was taking 0.382s, with enabled MMU it now takes
0.019s only or x20 improvement.

The time is proportional to the size of relocation, therefore if initramfs
is larger, 100M it could take over a second.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Tested-by: Pingfan Liu <piliu@redhat.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210930143113.1502553-13-pasha.tatashin@soleen.com
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 20 insertions, 11 deletions

diff --git a/arch/arm64/kernel/relocate_kernel.S b/arch/arm64/kernel/relocate_kernel.S
index 2b80232246f7..f0a3df9e18a3 100644
--- a/arch/arm64/kernel/relocate_kernel.S
+++ b/arch/arm64/kernel/relocate_kernel.S
@@ -4,6 +4,8 @@
  *
  * Copyright (C) Linaro.
  * Copyright (C) Huawei Futurewei Technologies.
+ * Copyright (C) 2021, Microsoft Corporation.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
  */
 
 #include <linux/kexec.h>
@@ -15,6 +17,13 @@
 #include <asm/sysreg.h>
 #include <asm/virt.h>
 
+.macro turn_off_mmu tmp1, tmp2
+	mov_q   \tmp1, INIT_SCTLR_EL1_MMU_OFF
+	pre_disable_mmu_workaround
+	msr	sctlr_el1, \tmp1
+	isb
+.endm
+
 .section    ".kexec_relocate.text", "ax"
 /*
  * arm64_relocate_new_kernel - Put a 2nd stage image in place and boot it.
@@ -32,22 +41,21 @@ SYM_CODE_START(arm64_relocate_new_kernel)
 	ldr	x18, [x0, #KIMAGE_ARCH_ZERO_PAGE] /* x18 = zero page for BBM */
 	ldr	x17, [x0, #KIMAGE_ARCH_TTBR1]	/* x17 = linear map copy */
 	ldr	x16, [x0, #KIMAGE_HEAD]		/* x16 = kimage_head */
-	mov	x14, xzr			/* x14 = entry ptr */
-	mov	x13, xzr			/* x13 = copy dest */
+	ldr	x22, [x0, #KIMAGE_ARCH_PHYS_OFFSET]	/* x22 phys_offset */
 	raw_dcache_line_size x15, x1		/* x15 = dcache line size */
 	break_before_make_ttbr_switch	x18, x17, x1, x2 /* set linear map */
 .Lloop:
 	and	x12, x16, PAGE_MASK		/* x12 = addr */
-
+	sub	x12, x12, x22			/* Convert x12 to virt */
 	/* Test the entry flags. */
 .Ltest_source:
 	tbz	x16, IND_SOURCE_BIT, .Ltest_indirection
 
 	/* Invalidate dest page to PoC. */
-	mov	x2, x13
-	add	x1, x2, #PAGE_SIZE
-	dcache_by_myline_op ivac, sy, x2, x1, x15, x20
+	mov	x19, x13
 	copy_page x13, x12, x1, x2, x3, x4, x5, x6, x7, x8
+	add	x1, x19, #PAGE_SIZE
+	dcache_by_myline_op civac, sy, x19, x1, x15, x20
 	b	.Lnext
 .Ltest_indirection:
 	tbz	x16, IND_INDIRECTION_BIT, .Ltest_destination
@@ -64,19 +72,20 @@ SYM_CODE_START(arm64_relocate_new_kernel)
 	ic	iallu
 	dsb	nsh
 	isb
+	ldr	x4, [x0, #KIMAGE_START]			/* relocation start */
+	ldr	x1, [x0, #KIMAGE_ARCH_EL2_VECTORS]	/* relocation start */
+	ldr	x0, [x0, #KIMAGE_ARCH_DTB_MEM]		/* dtb address */
+	turn_off_mmu x12, x13
 
 	/* Start new image. */
-	ldr	x1, [x0, #KIMAGE_ARCH_EL2_VECTORS]	/* relocation start */
 	cbz	x1, .Lel1
-	ldr	x1, [x0, #KIMAGE_START]		/* relocation start */
-	ldr	x2, [x0, #KIMAGE_ARCH_DTB_MEM]	/* dtb address */
+	mov	x1, x4				/* relocation start */
+	mov	x2, x0				/* dtb address */
 	mov	x3, xzr
 	mov	x4, xzr
 	mov     x0, #HVC_SOFT_RESTART
 	hvc	#0				/* Jumps from el2 */
 .Lel1:
-	ldr	x4, [x0, #KIMAGE_START]		/* relocation start */
-	ldr	x0, [x0, #KIMAGE_ARCH_DTB_MEM]	/* dtb address */
 	mov	x2, xzr
 	mov	x3, xzr
 	br	x4				/* Jumps from el1 */