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SubjectRe: [PATCH v2 4/8] KVM: VMX: Optimize vmx_set_rflags() for unrestricted guest
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On 09/10/19 18:38, Sean Christopherson wrote:
> 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?

If it's okay for you I can squash it.

Paolo

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