| Message ID | 20190926214302.21990-3-sean.j.christopherson@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: nVMX: Bug fix for consuming stale vmcs02.GUEST_CR3 | expand |
Sean Christopherson <sean.j.christopherson@intel.com> writes: > Skip the VMWRITE to update GUEST_CR3 if CR3 is not available, i.e. has > not been read from the VMCS since the last VM-Enter. If vcpu->arch.cr3 > is stale, kvm_read_cr3(vcpu) will refresh vcpu->arch.cr3 from the VMCS, > meaning KVM will do a VMREAD and then VMWRITE the value it just pulled > from the VMCS. > > Note, this is a purely theoretical change, no instances of skipping > the VMREAD+VMWRITE have been observed with this change. > > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> > --- > arch/x86/kvm/vmx/vmx.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index b530950a9c2b..6de09f60edf3 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -3003,10 +3003,12 @@ void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3) > > if (is_guest_mode(vcpu)) > skip_cr3 = true; > - else if (enable_unrestricted_guest || is_paging(vcpu)) > - guest_cr3 = kvm_read_cr3(vcpu); > - else > + else if (!enable_unrestricted_guest && !is_paging(vcpu)) > guest_cr3 = to_kvm_vmx(kvm)->ept_identity_map_addr; > + else if (test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail)) Nit: with 'test_bit(,(ulong *)&vcpu->arch.regs_avail)' spreading more and more I'd suggest creating an inline in kvm_cache_regs.h (e.g. kvm_vcpu_reg_avail()). > + guest_cr3 = vcpu->arch.cr3; > + else > + skip_cr3 = true; /* vmcs01.GUEST_CR3 is up-to-date. */ > ept_load_pdptrs(vcpu); > }
On Fri, Sep 27, 2019 at 02:11:27PM +0200, Vitaly Kuznetsov wrote: > Sean Christopherson <sean.j.christopherson@intel.com> writes: > > > Skip the VMWRITE to update GUEST_CR3 if CR3 is not available, i.e. has > > not been read from the VMCS since the last VM-Enter. If vcpu->arch.cr3 > > is stale, kvm_read_cr3(vcpu) will refresh vcpu->arch.cr3 from the VMCS, > > meaning KVM will do a VMREAD and then VMWRITE the value it just pulled > > from the VMCS. > > > > Note, this is a purely theoretical change, no instances of skipping > > the VMREAD+VMWRITE have been observed with this change. > > > > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> > > --- > > arch/x86/kvm/vmx/vmx.c | 8 +++++--- > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > > index b530950a9c2b..6de09f60edf3 100644 > > --- a/arch/x86/kvm/vmx/vmx.c > > +++ b/arch/x86/kvm/vmx/vmx.c > > @@ -3003,10 +3003,12 @@ void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3) > > > > if (is_guest_mode(vcpu)) > > skip_cr3 = true; > > - else if (enable_unrestricted_guest || is_paging(vcpu)) > > - guest_cr3 = kvm_read_cr3(vcpu); > > - else > > + else if (!enable_unrestricted_guest && !is_paging(vcpu)) > > guest_cr3 = to_kvm_vmx(kvm)->ept_identity_map_addr; > > + else if (test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail)) > > Nit: with 'test_bit(,(ulong *)&vcpu->arch.regs_avail)' spreading more and > more I'd suggest creating an inline in kvm_cache_regs.h > (e.g. kvm_vcpu_reg_avail()). Part of me wants to keep it painful to discourage one-off checks, but yeah, a helper would be nice. > > + guest_cr3 = vcpu->arch.cr3; > > + else > > + skip_cr3 = true; /* vmcs01.GUEST_CR3 is up-to-date. */ > > ept_load_pdptrs(vcpu); > > } > > -- > Vitaly
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index b530950a9c2b..6de09f60edf3 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -3003,10 +3003,12 @@ void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3) if (is_guest_mode(vcpu)) skip_cr3 = true; - else if (enable_unrestricted_guest || is_paging(vcpu)) - guest_cr3 = kvm_read_cr3(vcpu); - else + else if (!enable_unrestricted_guest && !is_paging(vcpu)) guest_cr3 = to_kvm_vmx(kvm)->ept_identity_map_addr; + else if (test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail)) + guest_cr3 = vcpu->arch.cr3; + else + skip_cr3 = true; /* vmcs01.GUEST_CR3 is up-to-date. */ ept_load_pdptrs(vcpu); }
Skip the VMWRITE to update GUEST_CR3 if CR3 is not available, i.e. has not been read from the VMCS since the last VM-Enter. If vcpu->arch.cr3 is stale, kvm_read_cr3(vcpu) will refresh vcpu->arch.cr3 from the VMCS, meaning KVM will do a VMREAD and then VMWRITE the value it just pulled from the VMCS. Note, this is a purely theoretical change, no instances of skipping the VMREAD+VMWRITE have been observed with this change. Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> --- arch/x86/kvm/vmx/vmx.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)