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Date: Mon, 25 Jun 2018 09:49:08 -0700
From: hpa@...or.com
To: Randy Dunlap <rdunlap@...radead.org>,
Jan Beulich <JBeulich@...e.com>, mingo@...e.hu,
tglx@...utronix.de
CC: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86-64: use 32-bit XOR to zero registers
On June 25, 2018 9:33:35 AM PDT, Randy Dunlap <rdunlap@...radead.org> wrote:
>On 06/25/2018 03:25 AM, Jan Beulich wrote:
>> Some Intel CPUs don't recognize 64-bit XORs as zeroing idioms - use
>> 32-bit ones instead.
>
>Hmph. Is that considered a bug (errata)?
>
>URL/references?
>
>Are these changes really only zeroing the lower 32 bits of the
>register?
>and that's all that the code cares about?
>
>thanks.
>
>> Signed-off-by: Jan Beulich <jbeulich@...e.com>
>> ---
>> arch/x86/crypto/aegis128-aesni-asm.S | 2 +-
>> arch/x86/crypto/aegis128l-aesni-asm.S | 2 +-
>> arch/x86/crypto/aegis256-aesni-asm.S | 2 +-
>> arch/x86/crypto/aesni-intel_asm.S | 8 ++++----
>> arch/x86/crypto/aesni-intel_avx-x86_64.S | 4 ++--
>> arch/x86/crypto/morus1280-avx2-asm.S | 2 +-
>> arch/x86/crypto/morus1280-sse2-asm.S | 2 +-
>> arch/x86/crypto/morus640-sse2-asm.S | 2 +-
>> arch/x86/crypto/sha1_ssse3_asm.S | 2 +-
>> arch/x86/kernel/head_64.S | 2 +-
>> arch/x86/kernel/paravirt_patch_64.c | 2 +-
>> arch/x86/lib/memcpy_64.S | 2 +-
>> arch/x86/power/hibernate_asm_64.S | 2 +-
>> 13 files changed, 17 insertions(+), 17 deletions(-)
>>
>> --- 4.18-rc2/arch/x86/crypto/aegis128-aesni-asm.S
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/crypto/aegis128-aesni-asm.S
>> @@ -75,7 +75,7 @@
>> * %r9
>> */
>> __load_partial:
>> - xor %r9, %r9
>> + xor %r9d, %r9d
>> pxor MSG, MSG
>>
>> mov LEN, %r8
>> --- 4.18-rc2/arch/x86/crypto/aegis128l-aesni-asm.S
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/crypto/aegis128l-aesni-asm.S
>> @@ -66,7 +66,7 @@
>> * %r9
>> */
>> __load_partial:
>> - xor %r9, %r9
>> + xor %r9d, %r9d
>> pxor MSG0, MSG0
>> pxor MSG1, MSG1
>>
>> --- 4.18-rc2/arch/x86/crypto/aegis256-aesni-asm.S
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/crypto/aegis256-aesni-asm.S
>> @@ -59,7 +59,7 @@
>> * %r9
>> */
>> __load_partial:
>> - xor %r9, %r9
>> + xor %r9d, %r9d
>> pxor MSG, MSG
>>
>> mov LEN, %r8
>> --- 4.18-rc2/arch/x86/crypto/aesni-intel_asm.S
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/crypto/aesni-intel_asm.S
>> @@ -258,7 +258,7 @@ ALL_F: .octa 0xffffffffffffffffffff
>> .macro GCM_INIT Iv SUBKEY AAD AADLEN
>> mov \AADLEN, %r11
>> mov %r11, AadLen(%arg2) # ctx_data.aad_length = aad_length
>> - xor %r11, %r11
>> + xor %r11d, %r11d
>> mov %r11, InLen(%arg2) # ctx_data.in_length = 0
>> mov %r11, PBlockLen(%arg2) # ctx_data.partial_block_length = 0
>> mov %r11, PBlockEncKey(%arg2) # ctx_data.partial_block_enc_key = 0
>> @@ -286,7 +286,7 @@ ALL_F: .octa 0xffffffffffffffffffff
>> movdqu HashKey(%arg2), %xmm13
>> add %arg5, InLen(%arg2)
>>
>> - xor %r11, %r11 # initialise the data pointer offset as zero
>> + xor %r11d, %r11d # initialise the data pointer offset as zero
>> PARTIAL_BLOCK %arg3 %arg4 %arg5 %r11 %xmm8 \operation
>>
>> sub %r11, %arg5 # sub partial block data used
>> @@ -702,7 +702,7 @@ _no_extra_mask_1_\@:
>>
>> # GHASH computation for the last <16 Byte block
>> GHASH_MUL \AAD_HASH, %xmm13, %xmm0, %xmm10, %xmm11, %xmm5, %xmm6
>> - xor %rax,%rax
>> + xor %eax, %eax
>>
>> mov %rax, PBlockLen(%arg2)
>> jmp _dec_done_\@
>> @@ -737,7 +737,7 @@ _no_extra_mask_2_\@:
>>
>> # GHASH computation for the last <16 Byte block
>> GHASH_MUL \AAD_HASH, %xmm13, %xmm0, %xmm10, %xmm11, %xmm5, %xmm6
>> - xor %rax,%rax
>> + xor %eax, %eax
>>
>> mov %rax, PBlockLen(%arg2)
>> jmp _encode_done_\@
>> --- 4.18-rc2/arch/x86/crypto/aesni-intel_avx-x86_64.S
>> +++
>4.18-rc2-x86_64-32bit-XOR/arch/x86/crypto/aesni-intel_avx-x86_64.S
>> @@ -463,7 +463,7 @@ _get_AAD_rest_final\@:
>>
>> _get_AAD_done\@:
>> # initialize the data pointer offset as zero
>> - xor %r11, %r11
>> + xor %r11d, %r11d
>>
>> # start AES for num_initial_blocks blocks
>> mov arg5, %rax # rax = *Y0
>> @@ -1770,7 +1770,7 @@ _get_AAD_rest_final\@:
>>
>> _get_AAD_done\@:
>> # initialize the data pointer offset as zero
>> - xor %r11, %r11
>> + xor %r11d, %r11d
>>
>> # start AES for num_initial_blocks blocks
>> mov arg5, %rax # rax = *Y0
>> --- 4.18-rc2/arch/x86/crypto/morus1280-avx2-asm.S
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/crypto/morus1280-avx2-asm.S
>> @@ -113,7 +113,7 @@ ENDPROC(__morus1280_update_zero)
>> * %r9
>> */
>> __load_partial:
>> - xor %r9, %r9
>> + xor %r9d, %r9d
>> vpxor MSG, MSG, MSG
>>
>> mov %rcx, %r8
>> --- 4.18-rc2/arch/x86/crypto/morus1280-sse2-asm.S
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/crypto/morus1280-sse2-asm.S
>> @@ -235,7 +235,7 @@ ENDPROC(__morus1280_update_zero)
>> * %r9
>> */
>> __load_partial:
>> - xor %r9, %r9
>> + xor %r9d, %r9d
>> pxor MSG_LO, MSG_LO
>> pxor MSG_HI, MSG_HI
>>
>> --- 4.18-rc2/arch/x86/crypto/morus640-sse2-asm.S
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/crypto/morus640-sse2-asm.S
>> @@ -113,7 +113,7 @@ ENDPROC(__morus640_update_zero)
>> * %r9
>> */
>> __load_partial:
>> - xor %r9, %r9
>> + xor %r9d, %r9d
>> pxor MSG, MSG
>>
>> mov %rcx, %r8
>> --- 4.18-rc2/arch/x86/crypto/sha1_ssse3_asm.S
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/crypto/sha1_ssse3_asm.S
>> @@ -96,7 +96,7 @@
>> # cleanup workspace
>> mov $8, %ecx
>> mov %rsp, %rdi
>> - xor %rax, %rax
>> + xor %eax, %eax
>> rep stosq
>>
>> mov %rbp, %rsp # deallocate workspace
>> --- 4.18-rc2/arch/x86/kernel/head_64.S
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/kernel/head_64.S
>> @@ -235,7 +235,7 @@ ENTRY(secondary_startup_64)
>> * address given in m16:64.
>> */
>> pushq $.Lafter_lret # put return address on stack for unwinder
>> - xorq %rbp, %rbp # clear frame pointer
>> + xorl %ebp, %ebp # clear frame pointer
>> movq initial_code(%rip), %rax
>> pushq $__KERNEL_CS # set correct cs
>> pushq %rax # target address in negative space
>> --- 4.18-rc2/arch/x86/kernel/paravirt_patch_64.c
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/kernel/paravirt_patch_64.c
>> @@ -20,7 +20,7 @@ DEF_NATIVE(, mov64, "mov %rdi, %rax");
>>
>> #if defined(CONFIG_PARAVIRT_SPINLOCKS)
>> DEF_NATIVE(pv_lock_ops, queued_spin_unlock, "movb $0, (%rdi)");
>> -DEF_NATIVE(pv_lock_ops, vcpu_is_preempted, "xor %rax, %rax");
>> +DEF_NATIVE(pv_lock_ops, vcpu_is_preempted, "xor %eax, %eax");
>> #endif
>>
>> unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len)
>> --- 4.18-rc2/arch/x86/lib/memcpy_64.S
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/lib/memcpy_64.S
>> @@ -256,7 +256,7 @@ ENTRY(__memcpy_mcsafe)
>>
>> /* Copy successful. Return zero */
>> .L_done_memcpy_trap:
>> - xorq %rax, %rax
>> + xorl %eax, %eax
>> ret
>> ENDPROC(__memcpy_mcsafe)
>> EXPORT_SYMBOL_GPL(__memcpy_mcsafe)
>> --- 4.18-rc2/arch/x86/power/hibernate_asm_64.S
>> +++ 4.18-rc2-x86_64-32bit-XOR/arch/x86/power/hibernate_asm_64.S
>> @@ -137,7 +137,7 @@ ENTRY(restore_registers)
>> /* Saved in save_processor_state. */
>> lgdt saved_context_gdt_desc(%rax)
>>
>> - xorq %rax, %rax
>> + xorl %eax, %eax
>>
>> /* tell the hibernation core that we've just restored the memory */
>> movq %rax, in_suspend(%rip)
>>
>>
>>
Writing the low 32 bits zero-extends the result to 64 bits anyway.
--
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