Re: [PATCH] x86-64: use 32-bit XOR to zero registers

From: Randy Dunlap
Date: Mon Jun 25 2018 - 12:33:45 EST

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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@xxxxxxxx>
> ---
> 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)
>
>
>

--
~Randy

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