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Subject[PATCH v9 17/18] arm64: kexec: enable MMU during kexec relocation
Date
Now, that we have transitional page tables configured, temporarily enable
MMU to allow faster relocation of segments to final destination.

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: Pavel Tatashin <pasha.tatashin@soleen.com>
---
arch/arm64/kernel/relocate_kernel.S | 144 ++++++++++++++++++----------
1 file changed, 92 insertions(+), 52 deletions(-)

diff --git a/arch/arm64/kernel/relocate_kernel.S b/arch/arm64/kernel/relocate_kernel.S
index 6fd2fc0ef373..430e7512ced5 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) 2020, Microsoft Corporation.
+ * Pavel Tatashin <pasha.tatashin@soleen.com>
*/

#include <linux/kexec.h>
@@ -16,6 +18,56 @@

.globl kexec_relocate_code_start
kexec_relocate_code_start:
+/* Invalidae TLB */
+.macro tlb_invalidate
+ dsb sy
+ dsb ish
+ tlbi vmalle1
+ dsb ish
+ isb
+.endm
+
+/* Turn-off mmu at level specified by sctlr */
+.macro turn_off_mmu sctlr, tmp1, tmp2
+ mrs \tmp1, \sctlr
+ ldr \tmp2, =SCTLR_ELx_FLAGS
+ bic \tmp1, \tmp1, \tmp2
+ pre_disable_mmu_workaround
+ msr \sctlr, \tmp1
+ isb
+.endm
+
+/* Turn-on mmu at level specified by sctlr */
+.macro turn_on_mmu sctlr, tmp1, tmp2
+ mrs \tmp1, \sctlr
+ ldr \tmp2, =SCTLR_ELx_FLAGS
+ orr \tmp1, \tmp1, \tmp2
+ msr \sctlr, \tmp1
+ ic iallu
+ dsb nsh
+ isb
+.endm
+
+/*
+ * Set ttbr0 and ttbr1, called while MMU is disabled, so no need to temporarily
+ * set zero_page table. Invalidate TLB after new tables are set.
+ */
+.macro set_ttbr arg, tmp1, tmp2
+ ldr \tmp1, [\arg, #KEXEC_KRELOC_TRANS_TTBR0]
+ msr ttbr0_el1, \tmp1
+ ldr \tmp1, [\arg, #KEXEC_KRELOC_TRANS_TTBR1]
+ offset_ttbr1 \tmp1, \tmp2
+ msr ttbr1_el1, \tmp1
+ isb
+.endm
+
+/* Set T0SZ to match the requirements of idmap page */
+.macro set_tcr_t0sz arg, tmp1, tmp2
+ ldr \tmp2, [\arg, #KEXEC_KRELOC_TRANS_T0SZ]
+ mrs \tmp1, tcr_el1
+ bfi \tmp1, \tmp2, TCR_T0SZ_OFFSET, TCR_TxSZ_WIDTH
+ msr tcr_el1, \tmp1
+.endm

/*
* arm64_relocate_new_kernel - Put a 2nd stage image in place and boot it.
@@ -27,65 +79,53 @@ kexec_relocate_code_start:
* symbols arm64_relocate_new_kernel and arm64_relocate_new_kernel_end. The
* machine_kexec() routine will copy arm64_relocate_new_kernel to the kexec
* safe memory that has been set up to be preserved during the copy operation.
+ *
+ * This function temporarily enables MMU if kernel relocation is needed.
+ * Also, if we enter this function at EL2 on non-VHE kernel, we temporarily go
+ * to EL1 to enable MMU, and escalate back to EL2 at the end to do the jump to
+ * the new kernel. This is determined by presence of el2_vector.
*/
ENTRY(arm64_relocate_new_kernel)
- /* Clear the sctlr_el2 flags. */
- mrs x2, CurrentEL
- cmp x2, #CurrentEL_EL2
+ mrs x1, CurrentEL
+ cmp x1, #CurrentEL_EL2
b.ne 1f
- mrs x2, sctlr_el2
- ldr x1, =SCTLR_ELx_FLAGS
- bic x2, x2, x1
- pre_disable_mmu_workaround
- msr sctlr_el2, x2
- isb
-1: /* Check if the new image needs relocation. */
- ldr x16, [x0, #KEXEC_KRELOC_HEAD] /* x16 = kimage_head */
- tbnz x16, IND_DONE_BIT, .Ldone
- raw_dcache_line_size x15, x1 /* x15 = dcache line size */
-.Lloop:
- and x12, x16, PAGE_MASK /* x12 = addr */
- /* Test the entry flags. */
-.Ltest_source:
- tbz x16, IND_SOURCE_BIT, .Ltest_indirection
-
- /* Invalidate dest page to PoC. */
- mov x2, x13
- add x20, x2, #PAGE_SIZE
- sub x1, x15, #1
- bic x2, x2, x1
-2: dc ivac, x2
- add x2, x2, x15
- cmp x2, x20
- b.lo 2b
- dsb sy
-
- copy_page x13, x12, x1, x2, x3, x4, x5, x6, x7, x8
- b .Lnext
-.Ltest_indirection:
- tbz x16, IND_INDIRECTION_BIT, .Ltest_destination
- mov x14, x12 /* ptr = addr */
- b .Lnext
-.Ltest_destination:
- tbz x16, IND_DESTINATION_BIT, .Lnext
- mov x13, x12 /* dest = addr */
-.Lnext:
- ldr x16, [x14], #8 /* entry = *ptr++ */
- tbz x16, IND_DONE_BIT, .Lloop /* while (!(entry & DONE)) */
-.Ldone:
- /* wait for writes from copy_page to finish */
- dsb nsh
- ic iallu
- dsb nsh
- isb
-
- /* Start new image. */
- ldr x4, [x0, #KEXEC_KRELOC_ENTRY_ADDR] /* x4 = kimage_start */
+ turn_off_mmu sctlr_el2, x1, x2 /* Turn off MMU at EL2 */
+1: mov x20, xzr /* x20 will hold vector value */
+ ldr x11, [x0, #KEXEC_KRELOC_COPY_LEN]
+ cbz x11, 5f /* Check if need to relocate */
+ ldr x20, [x0, #KEXEC_KRELOC_EL2_VECTOR]
+ cbz x20, 2f /* need to reduce to EL1? */
+ msr vbar_el2, x20 /* el2_vector present, means */
+ adr x1, 2f /* we will do copy in el1 but */
+ msr elr_el2, x1 /* do final jump from el2 */
+ eret /* Reduce to EL1 */
+2: set_tcr_t0sz x0, x1, x2 /* Set t0sz for idmaped page */
+ set_ttbr x0, x1, x2 /* Set our page tables */
+ tlb_invalidate
+ ldr x1, [x0, #KEXEC_KRELOC_DST_ADDR]; /* arg is not idmapped so */
+ ldr x2, [x0, #KEXEC_KRELOC_SRC_ADDR]; /* read before MMU is on */
+ turn_on_mmu sctlr_el1, x3, x4 /* Turn MMU back on */
+ mov x12, x1 /* x12 dst backup */
+3: copy_page x1, x2, x3, x4, x5, x6, x7, x8, x9, x10
+ sub x11, x11, #PAGE_SIZE
+ cbnz x11, 3b /* page copy loop */
+ raw_dcache_line_size x2, x3 /* x2 = dcache line size */
+ sub x3, x2, #1 /* x3 = dcache_size - 1 */
+ bic x12, x12, x3
+4: dc cvau, x12 /* Flush D-cache */
+ add x12, x12, x2
+ cmp x12, x1 /* Compare to dst + len */
+ b.ne 4b /* D-cache flush loop */
+ turn_off_mmu sctlr_el1, x1, x2 /* Turn off MMU */
+ tlb_invalidate /* Invalidate TLB */
+5: ldr x4, [x0, #KEXEC_KRELOC_ENTRY_ADDR] /* x4 = kimage_start */
ldr x3, [x0, #KEXEC_KRELOC_KERN_ARG3]
ldr x2, [x0, #KEXEC_KRELOC_KERN_ARG2]
ldr x1, [x0, #KEXEC_KRELOC_KERN_ARG1]
ldr x0, [x0, #KEXEC_KRELOC_KERN_ARG0] /* x0 = dtb address */
- br x4
+ cbnz x20, 6f /* need to escalate to el2? */
+ br x4 /* Jump to new world */
+6: hvc #0 /* enters kexec_el1_sync */
.ltorg
END(arm64_relocate_new_kernel)

--
2.17.1
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