The following commit has been merged into the x86/boot branch of tip: Commit-ID: 721f791ce1cddfa5f2bf524ac14741bfa0f72697 Gitweb: https://git.kernel.org/tip/721f791ce1cddfa5f2bf524ac14741bfa0f72697 Author: Uros Bizjak <ubizjak@xxxxxxxxx> AuthorDate: Wed, 24 Jan 2024 11:38:59 +01:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Fri, 01 Mar 2024 12:47:37 +01:00 x86/boot: Use 32-bit XOR to clear registers x86_64 zero extends 32-bit operations, so for 64-bit operands, XORL r32,r32 is functionally equal to XORQ r64,r64, but avoids a REX prefix byte when legacy registers are used. Slightly smaller code generated, no change in functionality. Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Brian Gerst <brgerst@xxxxxxxxx> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx> Link: https://lore.kernel.org/r/20240124103859.611372-1-ubizjak@xxxxxxxxx --- arch/x86/kernel/head_64.S | 6 +++--- arch/x86/kernel/sev_verify_cbit.S | 2 +- 2 files changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index d295bf6..86136a7 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -169,7 +169,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) ANNOTATE_NOENDBR /* Clear %R15 which holds the boot_params pointer on the boot CPU */ - xorq %r15, %r15 + xorl %r15d, %r15d /* * Retrieve the modifier (SME encryption mask if SME is active) to be @@ -178,7 +178,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) #ifdef CONFIG_AMD_MEM_ENCRYPT movq sme_me_mask, %rax #else - xorq %rax, %rax + xorl %eax, %eax #endif /* Form the CR3 value being sure to include the CR3 modifier */ @@ -295,7 +295,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) .Llookup_AP: /* EAX contains the APIC ID of the current CPU */ - xorq %rcx, %rcx + xorl %ecx, %ecx leaq cpuid_to_apicid(%rip), %rbx .Lfind_cpunr: diff --git a/arch/x86/kernel/sev_verify_cbit.S b/arch/x86/kernel/sev_verify_cbit.S index 3355e27..1ab65f6 100644 --- a/arch/x86/kernel/sev_verify_cbit.S +++ b/arch/x86/kernel/sev_verify_cbit.S @@ -77,7 +77,7 @@ SYM_FUNC_START(sev_verify_cbit) * The check failed, prevent any forward progress to prevent ROP * attacks, invalidate the stack and go into a hlt loop. */ - xorq %rsp, %rsp + xorl %esp, %esp subq $0x1000, %rsp 2: hlt jmp 2b
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