ARM: decompressor: use by-VA cache maintenance for v7 cores
Subsystems (2)
Ard Biesheuvel
maintainerv3 cover ARM: decompressor: use by-VA cache maintenance for v7 cores
While making changes to the EFI stub startup code, I noticed that we are still doing set/way maintenance on the caches when booting on v7 cores. This works today on VMs by virtue of the fact that KVM traps set/way ops and cleans the whole address space by VA on behalf of the guest, and on most v7 hardware, the set/way ops are in fact sufficient when only one core is running, as there usually is no system cache. But on systems like SynQuacer, for which 32-bit firmware is available, the current cache maintenance only pushes the data out to the L3 system cache, where it is not visible to the CPU once it turns the MMU and caches off.
So instead, switch to the by-VA cache maintenance that the architecture requires for v7 and later (and ARM1176, as a side effect).
Changes since v2:
- add a patch to factor out the code sequence that obtains the inflated image size by doing an unaligned LE32 load from the end of the compressed data
- use new macro to load the inflated image size instead of doing a potentially unaligned load
- omit the stack for getting the base and size of the self-relocated zImage
Changes since v1:
- include the EFI patch that was sent out separately before (#1)
- split the preparatory work to pass the region to clean in r0/r1 in a EFI specific one and one for the decompressor - this way, the first two patches can go on a stable branch that is shared between the ARM tree and the EFI tree
- document the meaning of the values in r0/r1 upon entry to cache_clean_flush
- take care to treat the region end address as exclusive
- switch to clean+invalidate to align with the other implementations
- drop some code that manages the stack pointer value before calling cache_clean_flush(), which is no longer necessary
- take care to clean the entire region that is covered by the relocated zImage if it needs to relocate itself before decompressing
https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/?h=arm32-efi-cache-ops
[ Several people asked me offline why on earth I am running SynQuacer on 32 bit:
the answer is that this is simply to prove that it is currently broken, and this implies that for 32-bit VMs running under KVM, we are relying on the special, non-architectural cache management done by the hypervisor on behalf of the guest to be able to run this code. ]
Ard Biesheuvel (5):
efi/arm: Work around missing cache maintenance in decompressor
handover
efi/arm: Pass start and end addresses to cache_clean_flush()
ARM: decompressor: factor out routine to obtain the inflated image
size
ARM: decompressor: prepare cache_clean_flush for doing by-VA
maintenance
ARM: decompressor: switch to by-VA cache maintenance for v7 cores
arch/arm/boot/compressed/head.S | 166 +++++++++++--------- 1 file changed, 91 insertions(+), 75 deletions(-)
Signature · 1 line
2.17.1
Ard Biesheuvel
maintainerPATCH v3 1/5 efi/arm: Work around missing cache maintenance in decompressor handover
The EFI stub executes within the context of the zImage as it was loaded by the firmware, which means it is treated as an ordinary PE/COFF executable, which is loaded into memory, and cleaned to the PoU to ensure that it can be executed safely while the MMU and caches are on.
When the EFI stub hands over to the decompressor, we clean the caches by set/way and disable the MMU and D-cache, to comply with the Linux boot protocol for ARM. However, cache maintenance by set/way is not sufficient to ensure that subsequent instruction fetches and data accesses done with the MMU off see the correct data. This means that proceeding as we do currently is not safe, especially since we also perform data accesses with the MMU off, from a literal pool as well as the stack.
So let's kick this can down the road a bit, and jump into the relocated zImage before disabling the caches. This removes the requirement to perform any by-VA cache maintenance on the original PE/COFF executable, but it does require that the relocated zImage is cleaned to the PoC, which is currently not the case. This will be addressed in a subsequent patch.
--- arch/arm/boot/compressed/head.S | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-)
arch/arm/boot/compressed/head.S +14 -6
@@ -1461,6 +1461,17 @@ ENTRY(efi_stub_entry) @ Preserve return value of efi_entry() in r4 mov r4, r0 bl cache_clean_flush + + @ The PE/COFF loader might not have cleaned the code we are + @ running beyond the PoU, and so calling cache_off below from + @ inside the PE/COFF loader allocated region is unsafe. Let's + @ assume our own zImage relocation code did a better job, and + @ jump into its version of this routine before proceeding. + ldr r0, [sp] @ relocated zImage + ldr r1, .Ljmp + sub r1, r0, r1 + mov pc, r1 @ no mode switch +0: bl cache_off @ Set parameters for booting zImage according to boot protocol
@@ -1469,18 +1480,15 @@ ENTRY(efi_stub_entry) mov r0, #0 mov r1, #0xFFFFFFFF mov r2, r4 - - @ Branch to (possibly) relocated zImage that is in [sp] - ldr lr, [sp] - ldr ip, =start_offset - add lr, lr, ip - mov pc, lr @ no mode switch + b __efi_start efi_load_fail: @ Return EFI_LOAD_ERROR to EFI firmware on error. ldr r0, =0x80000001 ldmfd sp!, {ip, pc} ENDPROC(efi_stub_entry) + .align 2 +.Ljmp: .long start - 0b #endif .align
Signature · 1 line
2.17.1
Ard Biesheuvel
maintainerPATCH v3 2/5 efi/arm: Pass start and end addresses to cache_clean_flush()
In reply to Ard BiesheuvelIn preparation for turning the decompressor's cache clean/flush operations into proper by-VA maintenance for v7 cores, pass the start and end addresses of the regions that need cache maintenance into cache_clean_flush in registers r0 and r1.
Currently, all implementations of cache_clean_flush ignore these values, so no functional change is expected as a result of this patch.
--- arch/arm/boot/compressed/head.S | 6 ++++++ 1 file changed, 6 insertions(+)
arch/arm/boot/compressed/head.S +6 -0
@@ -1460,6 +1460,12 @@ ENTRY(efi_stub_entry) @ Preserve return value of efi_entry() in r4 mov r4, r0 + add r1, r4, #SZ_2M @ DT end + bl cache_clean_flush + + ldr r0, [sp] @ relocated zImage + ldr r1, =_edata @ size of zImage + add r1, r1, r0 @ end of zImage bl cache_clean_flush @ The PE/COFF loader might not have cleaned the code we are
Signature · 1 line
2.17.1
Ard Biesheuvel
maintainerPATCH v3 3/5 ARM: decompressor: factor out routine to obtain the inflated image size
In reply to Ard BiesheuvelBefore adding another reference to the inflated image size, factor out the slightly complicated way of loading the unaligned little-endian constant from the end of the compressed data.
--- arch/arm/boot/compressed/head.S | 43 ++++++++++++-------- 1 file changed, 26 insertions(+), 17 deletions(-)
arch/arm/boot/compressed/head.S +26 -17
@@ -151,6 +151,25 @@ .L_\@: .endm + /* + * The kernel build system appends the size of the + * decompressed kernel at the end of the compressed data + * in little-endian form. + */ + .macro get_inflated_image_size, res:req, tmp1:req, tmp2:req + adr \res, .Linflated_image_size_offset + ldr \tmp1, [\res] + add \tmp1, \tmp1, \res @ offset of inflated image size + + ldrb \res, [\tmp1] @ get_unaligned_le32 + ldrb \tmp2, [\tmp1, #1] + orr \res, \res, \tmp2, lsl #8 + ldrb \tmp2, [\tmp1, #2] + ldrb \tmp1, [\tmp1, #3] + orr \res, \res, \tmp2, lsl #16 + orr \res, \res, \tmp1, lsl #24 + .endm + .section ".start", "ax" /* * sort out different calling conventions
@@ -268,15 +287,15 @@ not_angel: */ mov r0, pc cmp r0, r4 - ldrcc r0, LC0+32 + ldrcc r0, LC0+28 addcc r0, r0, pc cmpcc r4, r0 orrcc r4, r4, #1 @ remember we skipped cache_on blcs cache_on restart: adr r0, LC0 - ldmia r0, {r1, r2, r3, r6, r10, r11, r12} - ldr sp, [r0, #28] + ldmia r0, {r1, r2, r3, r6, r11, r12} + ldr sp, [r0, #24] /* * We might be running at a different address. We need
@@ -284,20 +303,8 @@ restart: adr r0, LC0 */ sub r0, r0, r1 @ calculate the delta offset add r6, r6, r0 @ _edata - add r10, r10, r0 @ inflated kernel size location - /* - * The kernel build system appends the size of the - * decompressed kernel at the end of the compressed data - * in little-endian form. - */ - ldrb r9, [r10, #0] - ldrb lr, [r10, #1] - orr r9, r9, lr, lsl #8 - ldrb lr, [r10, #2] - ldrb r10, [r10, #3] - orr r9, r9, lr, lsl #16 - orr r9, r9, r10, lsl #24 + get_inflated_image_size r9, r10, lr #ifndef CONFIG_ZBOOT_ROM /* malloc space is above the relocated stack (64k max) */
@@ -652,13 +659,15 @@ LC0: .word LC0 @ r1 .word __bss_start @ r2 .word _end @ r3 .word _edata @ r6 - .word input_data_end - 4 @ r10 (inflated size location) .word _got_start @ r11 .word _got_end @ ip .word .L_user_stack_end @ sp .word _end - restart + 16384 + 1024*1024 .size LC0, . - LC0 +.Linflated_image_size_offset: + .long (input_data_end - 4) - . + #ifdef CONFIG_ARCH_RPC .globl params params: ldr r0, =0x10000100 @ params_phys for RPC
Signature · 1 line
2.17.1
Ard Biesheuvel
maintainerPATCH v3 4/5 ARM: decompressor: prepare cache_clean_flush for doing by-VA maintenance
In reply to Ard BiesheuvelIn preparation for turning the decompressor's cache clean/flush operations into proper by-VA maintenance for v7 cores, pass the start and end addresses of the regions that need cache maintenance into cache_clean_flush in registers r0 and r1.
Currently, all implementations of cache_clean_flush ignore these values, so no functional change is expected as a result of this patch.
--- arch/arm/boot/compressed/head.S | 15 +++++++++++++++ 1 file changed, 15 insertions(+)
arch/arm/boot/compressed/head.S +15 -0
@@ -533,12 +533,19 @@ dtb_check_done: add sp, sp, r6 #endif + adr r0, restart + ldr r1, .Lclean_size + add r0, r0, r6 + add r1, r1, r0 bl cache_clean_flush badr r0, restart add r0, r0, r6 mov pc, r0 + .align 2 +.Lclean_size: .long _edata - restart + wont_overwrite: /* * If delta is zero, we are running at the address we were linked at.
@@ -629,6 +636,11 @@ not_relocated: mov r0, #0 add r2, sp, #0x10000 @ 64k max mov r3, r7 bl decompress_kernel + + get_inflated_image_size r1, r2, r3 + + mov r0, r4 @ start of inflated image + add r1, r1, r0 @ end of inflated image bl cache_clean_flush bl cache_off
@@ -1182,6 +1194,9 @@ __armv7_mmu_cache_off: /* * Clean and flush the cache to maintain consistency. * + * On entry, + * r0 = start address + * r1 = end address (exclusive) * On exit, * r1, r2, r3, r9, r10, r11, r12 corrupted * This routine must preserve:
Signature · 1 line
2.17.1
Ard Biesheuvel
maintainerPATCH v3 5/5 ARM: decompressor: switch to by-VA cache maintenance for v7 cores
In reply to Ard BiesheuvelUpdate the v7 cache_clean_flush routine to take into account the memory range passed in r0/r1, and perform cache maintenance by virtual address on this range instead of set/way maintenance, which is inappropriate for the purpose of maintaining the cached state of memory contents.
Since this removes any use of the stack in the implementation of cache_clean_flush(), we can also drop some code that manages the value of the stack pointer before calling it.
--- arch/arm/boot/compressed/head.S | 82 +++++++------------- 1 file changed, 30 insertions(+), 52 deletions(-)
arch/arm/boot/compressed/head.S +30 -52
@@ -528,10 +528,6 @@ dtb_check_done: /* Preserve offset to relocated code. */ sub r6, r9, r6 -#ifndef CONFIG_ZBOOT_ROM - /* cache_clean_flush may use the stack, so relocate it */ - add sp, sp, r6 -#endif adr r0, restart ldr r1, .Lclean_size
@@ -688,6 +684,24 @@ params: ldr r0, =0x10000100 @ params_phys for RPC .align #endif +/* + * dcache_line_size - get the minimum D-cache line size from the CTR register + * on ARMv7. + */ + .macro dcache_line_size, reg, tmp +#ifdef CONFIG_CPU_V7M + movw \tmp, #:lower16:BASEADDR_V7M_SCB + V7M_SCB_CTR + movt \tmp, #:upper16:BASEADDR_V7M_SCB + V7M_SCB_CTR + ldr \tmp, [\tmp] +#else + mrc p15, 0, \tmp, c0, c0, 1 @ read ctr +#endif + lsr \tmp, \tmp, #16 + and \tmp, \tmp, #0xf @ cache line size encoding + mov \reg, #4 @ bytes per word + mov \reg, \reg, lsl \tmp @ actual cache line size + .endm + /* * Turn on the cache. We need to setup some page tables so that we * can have both the I and D caches on.
@@ -1180,8 +1194,6 @@ __armv7_mmu_cache_off: bic r0, r0, #0x000c #endif mcr p15, 0, r0, c1, c0 @ turn MMU and cache off - mov r12, lr - bl __armv7_mmu_cache_flush mov r0, #0 #ifdef CONFIG_MMU mcr p15, 0, r0, c8, c7, 0 @ invalidate whole TLB
@@ -1189,7 +1201,7 @@ __armv7_mmu_cache_off: mcr p15, 0, r0, c7, c5, 6 @ invalidate BTC mcr p15, 0, r0, c7, c10, 4 @ DSB mcr p15, 0, r0, c7, c5, 4 @ ISB - mov pc, r12 + mov pc, lr /* * Clean and flush the cache to maintain consistency.
@@ -1205,6 +1217,7 @@ __armv7_mmu_cache_off: .align 5 cache_clean_flush: mov r3, #16 + mov r11, r1 b call_cache_fn __armv4_mpu_cache_flush:
@@ -1255,51 +1268,16 @@ __armv7_mmu_cache_flush: mcr p15, 0, r10, c7, c14, 0 @ clean+invalidate D b iflush hierarchical: - mcr p15, 0, r10, c7, c10, 5 @ DMB - stmfd sp!, {r0-r7, r9-r11} - mrc p15, 1, r0, c0, c0, 1 @ read clidr - ands r3, r0, #0x7000000 @ extract loc from clidr - mov r3, r3, lsr #23 @ left align loc bit field - beq finished @ if loc is 0, then no need to clean - mov r10, #0 @ start clean at cache level 0 -loop1: - add r2, r10, r10, lsr #1 @ work out 3x current cache level - mov r1, r0, lsr r2 @ extract cache type bits from clidr - and r1, r1, #7 @ mask of the bits for current cache only - cmp r1, #2 @ see what cache we have at this level - blt skip @ skip if no cache, or just i-cache - mcr p15, 2, r10, c0, c0, 0 @ select current cache level in cssr - mcr p15, 0, r10, c7, c5, 4 @ isb to sych the new cssr&csidr - mrc p15, 1, r1, c0, c0, 0 @ read the new csidr - and r2, r1, #7 @ extract the length of the cache lines - add r2, r2, #4 @ add 4 (line length offset) - ldr r4, =0x3ff - ands r4, r4, r1, lsr #3 @ find maximum number on the way size - clz r5, r4 @ find bit position of way size increment - ldr r7, =0x7fff - ands r7, r7, r1, lsr #13 @ extract max number of the index size -loop2: - mov r9, r4 @ create working copy of max way size -loop3: - ARM( orr r11, r10, r9, lsl r5 ) @ factor way and cache number into r11 - ARM( orr r11, r11, r7, lsl r2 ) @ factor index number into r11 - THUMB( lsl r6, r9, r5 ) - THUMB( orr r11, r10, r6 ) @ factor way and cache number into r11 - THUMB( lsl r6, r7, r2 ) - THUMB( orr r11, r11, r6 ) @ factor index number into r11 - mcr p15, 0, r11, c7, c14, 2 @ clean & invalidate by set/way - subs r9, r9, #1 @ decrement the way - bge loop3 - subs r7, r7, #1 @ decrement the index - bge loop2 -skip: - add r10, r10, #2 @ increment cache number - cmp r3, r10 - bgt loop1 -finished: - ldmfd sp!, {r0-r7, r9-r11} - mov r10, #0 @ switch back to cache level 0 - mcr p15, 2, r10, c0, c0, 0 @ select current cache level in cssr + dcache_line_size r1, r2 @ r1 := dcache min line size + sub r2, r1, #1 @ r2 := line size mask + bic r0, r0, r2 @ round down start to line size + sub r11, r11, #1 @ end address is exclusive + bic r11, r11, r2 @ round down end to line size +0: cmp r0, r11 @ finished? + bgt iflush + mcr p15, 0, r0, c7, c14, 1 @ Dcache clean/invalidate by VA + add r0, r0, r1 + b 0b iflush: mcr p15, 0, r10, c7, c10, 4 @ DSB mcr p15, 0, r10, c7, c5, 0 @ invalidate I+BTB
Signature · 1 line
2.17.1
Quoted 10 lines · Ard Biesheuvel
While making changes to the EFI stub startup code, I noticed that we are still doing set/way maintenance on the caches when booting on v7 cores. This works today on VMs by virtue of the fact that KVM traps set/way ops and cleans the whole address space by VA on behalf of the guest, and on most v7 hardware, the set/way ops are in fact sufficient when only one core is running, as there usually is no system cache. But on systems like SynQuacer, for which 32-bit firmware is available, the current cache maintenance only pushes the data out to the L3 system cache, where it is not visible to the CPU once it turns the MMU and caches off.
Quoted 2 lines
So instead, switch to the by-VA cache maintenance that the architecture requires for v7 and later (and ARM1176, as a side effect).
I took this v3 patch set for a ride on some ARMv7 and ARMv6 (hardware) boards using zImage:s so the compressed path should be exercised:
- Ux500 (ARMv7 Cortex A9 x 2) works like a charm
- RealView PB11MPCore (ARM1176 x 4 MPCore) works like a charm
I can do more thorough tests with more boards if needed.
Yours,
Linus Walleij
Ard Biesheuvel
maintainerQuoted 20 lines · Linus Walleij
Quoted 10 lines · Ard Biesheuvel
While making changes to the EFI stub startup code, I noticed that we are still doing set/way maintenance on the caches when booting on v7 cores. This works today on VMs by virtue of the fact that KVM traps set/way ops and cleans the whole address space by VA on behalf of the guest, and on most v7 hardware, the set/way ops are in fact sufficient when only one core is running, as there usually is no system cache. But on systems like SynQuacer, for which 32-bit firmware is available, the current cache maintenance only pushes the data out to the L3 system cache, where it is not visible to the CPU once it turns the MMU and caches off.
Quoted 2 lines
So instead, switch to the by-VA cache maintenance that the architecture requires for v7 and later (and ARM1176, as a side effect).
I took this v3 patch set for a ride on some ARMv7 and ARMv6 (hardware) boards using zImage:s so the compressed path should be exercised:
Quoted 7 lines
- Ux500 (ARMv7 Cortex A9 x 2) works like a charm
- RealView PB11MPCore (ARM1176 x 4 MPCore) works like a charmTested-by Linus Walleij <[email protected]>I can do more thorough tests with more boards if needed.
Thanks Linus. Do you happen to have any boards that boot with appended DTB?
Ard Biesheuvel
maintainerQuoted 25 lines · Ard Biesheuvel
Quoted 23 lines · Linus Walleij
Quoted 10 lines · Ard Biesheuvel
While making changes to the EFI stub startup code, I noticed that we are still doing set/way maintenance on the caches when booting on v7 cores. This works today on VMs by virtue of the fact that KVM traps set/way ops and cleans the whole address space by VA on behalf of the guest, and on most v7 hardware, the set/way ops are in fact sufficient when only one core is running, as there usually is no system cache. But on systems like SynQuacer, for which 32-bit firmware is available, the current cache maintenance only pushes the data out to the L3 system cache, where it is not visible to the CPU once it turns the MMU and caches off.
Quoted 2 lines
So instead, switch to the by-VA cache maintenance that the architecture requires for v7 and later (and ARM1176, as a side effect).
I took this v3 patch set for a ride on some ARMv7 and ARMv6 (hardware) boards using zImage:s so the compressed path should be exercised:
- Ux500 (ARMv7 Cortex A9 x 2) works like a charm
- RealView PB11MPCore (ARM1176 x 4 MPCore) works like a charm
Quoted 6 lines
Quoted 4 lines
Tested-by Linus Walleij <[email protected]>I can do more thorough tests with more boards if needed.
Thanks Linus. Do you happen to have any boards that boot with appended DTB?
Actually, I can easily test that myself as well in QEMU.
Quoted 6 lines · Ard Biesheuvel
Quoted 4 lines · Linus Walleij
I took this v3 patch set for a ride on some ARMv7 and ARMv6 (hardware) boards using zImage:s so the compressed path should be exercised:
Quoted 8 lines
Quoted 6 lines
- Ux500 (ARMv7 Cortex A9 x 2) works like a charm
- RealView PB11MPCore (ARM1176 x 4 MPCore) works like a charmTested-by Linus Walleij <[email protected]>I can do more thorough tests with more boards if needed.
Thanks Linus. Do you happen to have any boards that boot with appended DTB?
Oh, both of these use appended DTB so it's definitely working.
Yours,
Linus Walleij