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SubjectRe: [PATCH v2 4/8] KVM: VMX: Optimize vmx_set_rflags() for unrestricted guest
On Wed, Oct 09, 2019 at 12:40:53PM +0200, Paolo Bonzini wrote:
> On 27/09/19 23:45, Sean Christopherson wrote:
> > Rework vmx_set_rflags() to avoid the extra code need to handle emulation
> > of real mode and invalid state when unrestricted guest is disabled. The
> > primary reason for doing so is to avoid the call to vmx_get_rflags(),
> > which will incur a VMREAD when RFLAGS is not already available. When
> > running nested VMs, the majority of calls to vmx_set_rflags() will occur
> > without an associated vmx_get_rflags(), i.e. when stuffing GUEST_RFLAGS
> > during transitions between vmcs01 and vmcs02.
> >
> > Note, vmx_get_rflags() guarantees RFLAGS is marked available.
>
> Slightly nicer this way:
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 8de9853d7ab6..62ab19d65efd 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1431,9 +1431,17 @@ unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
> void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
> {
> struct vcpu_vmx *vmx = to_vmx(vcpu);
> - unsigned long old_rflags = vmx_get_rflags(vcpu);
> + unsigned long old_rflags;
> +
> + if (enable_unrestricted_guest) {
> + __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
> + vmx->rflags = rflags;
> + vmcs_writel(GUEST_RFLAGS, rflags);
> + return;
> + }
> +
> + old_rflags = vmx_get_rflags(vcpu);
>
> - __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
> vmx->rflags = rflags;
> if (vmx->rmode.vm86_active) {
> vmx->rmode.save_rflags = rflags;

Works for me. Do you want me to spin a v3 to incorporate this and remove
the open coding of the RIP/RSP accessors? Or are you planning on squashing
the changes as you apply?

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