From 898a811f1486df3209ce857027d0564d6a616cf2 Mon Sep 17 00:00:00 2001 From: Jim Mattson Date: Wed, 5 Dec 2018 15:28:59 -0800 Subject: [PATCH] kvm: vmx: Document the need for MSR_STAR in i386 builds Add a comment explaining why MSR_STAR must be included in vmx_msr_index[] even for i386 builds. The elided comment has not been relevant since move_msr_up() was introduced in commit a75beee6e4f5d ("KVM: VMX: Avoid saving and restoring msrs on lightweight vmexit"). Signed-off-by: Jim Mattson Reviewed-by: Peter Shier Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx/vmx.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index c1feb62faac4..d754fd0c8674 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -373,8 +373,11 @@ static const struct kvm_vmx_segment_field { u64 host_efer; /* - * Keep MSR_STAR at the end, as setup_msrs() will try to optimize it - * away by decrementing the array size. + * Though SYSCALL is only supported in 64-bit mode on Intel CPUs, kvm + * will emulate SYSCALL in legacy mode if the vendor string in guest + * CPUID.0:{EBX,ECX,EDX} is "AuthenticAMD" or "AMDisbetter!" To + * support this emulation, IA32_STAR must always be included in + * vmx_msr_index[], even in i386 builds. */ const u32 vmx_msr_index[] = { #ifdef CONFIG_X86_64 -- GitLab