diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2024-01-24 11:38:59 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2024-03-01 12:47:37 +0100 |
| commit | 721f791ce1cddfa5f2bf524ac14741bfa0f72697 (patch) | |
| tree | d3e38ba1c8505147a4fbf5c1c3202a26ea486908 /arch | |
| parent | 891f8890a4a3663da7056542757022870b499bc1 (diff) | |
| download | linux-721f791ce1cddfa5f2bf524ac14741bfa0f72697.tar.gz | |
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@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240124103859.611372-1-ubizjak@gmail.com
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/head_64.S | 6 | ||||
| -rw-r--r-- | 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 d295bf68bf944f..86136a78778e85 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 3355e27c69ebf8..1ab65f6c6ae7a1 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 |