On 4/10/2025 4:24 PM, Sean Christopherson wrote:
+/*
+ * 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().
Will do.
