On Mon, Mar 31, 2025, Xin Li (Intel) wrote: > Signed-off-by: Xin Li (Intel) <xin@xxxxxxxxx> > --- > arch/x86/include/asm/msr-index.h | 6 ++++++ > arch/x86/kvm/vmx/vmenter.S | 28 ++++++++++++++++++++++++---- > 2 files changed, 30 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h > index e6134ef2263d..04244c3ba374 100644 > --- a/arch/x86/include/asm/msr-index.h > +++ b/arch/x86/include/asm/msr-index.h > @@ -1226,4 +1226,10 @@ > * a #GP > */ > > +/* Instruction opcode for WRMSRNS supported in binutils >= 2.40 */ > +#define ASM_WRMSRNS _ASM_BYTES(0x0f,0x01,0xc6) > + > +/* Instruction opcode for the immediate form RDMSR/WRMSRNS */ > +#define ASM_WRMSRNS_RAX _ASM_BYTES(0xc4,0xe7,0x7a,0xf6,0xc0) > + > #endif /* _ASM_X86_MSR_INDEX_H */ > diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S > index f6986dee6f8c..9fae43723c44 100644 > --- a/arch/x86/kvm/vmx/vmenter.S > +++ b/arch/x86/kvm/vmx/vmenter.S > @@ -64,6 +64,29 @@ > RET > .endm > > +/* > + * Write EAX to MSR_IA32_SPEC_CTRL. > + * > + * Choose the best WRMSR instruction based on availability. > + * > + * Replace with 'wrmsrns' and 'wrmsrns %rax, $MSR_IA32_SPEC_CTRL' once binutils support them. > + */ > +.macro WRITE_EAX_TO_MSR_IA32_SPEC_CTRL > + ALTERNATIVE_2 __stringify(mov $MSR_IA32_SPEC_CTRL, %ecx; \ > + xor %edx, %edx; \ > + mov %edi, %eax; \ > + ds wrmsr), \ > + __stringify(mov $MSR_IA32_SPEC_CTRL, %ecx; \ > + xor %edx, %edx; \ > + mov %edi, %eax; \ > + ASM_WRMSRNS), \ > + X86_FEATURE_WRMSRNS, \ > + __stringify(xor %_ASM_AX, %_ASM_AX; \ > + mov %edi, %eax; \ > + ASM_WRMSRNS_RAX; .long MSR_IA32_SPEC_CTRL), \ > + X86_FEATURE_MSR_IMM > +.endm This is quite hideous. I have no objection to optimizing __vmx_vcpu_run(), but I would much prefer that a macro like this live in generic code, and that it be generic. It should be easy enough to provide an assembly friendly equivalent to __native_wrmsr_constant(). > + > .section .noinstr.text, "ax" > > /** > @@ -123,10 +146,7 @@ SYM_FUNC_START(__vmx_vcpu_run) > movl PER_CPU_VAR(x86_spec_ctrl_current), %esi > cmp %edi, %esi > je .Lspec_ctrl_done > - mov $MSR_IA32_SPEC_CTRL, %ecx > - xor %edx, %edx > - mov %edi, %eax > - wrmsr > + WRITE_EAX_TO_MSR_IA32_SPEC_CTRL > > .Lspec_ctrl_done: > > -- > 2.49.0 >
