| Message ID | 20210424004645.3950558-23-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: vCPU RESET/INIT fixes and consolidation | expand |
On Fri, Apr 23, 2021 at 5:51 PM Sean Christopherson <seanjc@google.com> wrote: > > Remove a bogus write to vcpu->arch.cr0 that immediately precedes > vmx_set_cr0() during vCPU RESET/INIT. For RESET, this is a nop since > the "old" CR0 value is meaningless. But for INIT, if the vCPU is coming > from paging enabled mode, crushing vcpu->arch.cr0 will cause the various > is_paging() checks in vmx_set_cr0() to get false negatives. > > For the exit_lmode() case, the false negative is benign as vmx_set_efer() > is called immediately after vmx_set_cr0(). > > For EPT without unrestricted guest, the false negative will cause KVM to > unnecessarily run with CR3 load/store exiting. But again, this is > benign, albeit sub-optimal. > > Signed-off-by: Sean Christopherson <seanjc@google.com> Reviewed-by: Reiji Watanabe <reijiw@google.com>
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index d0050c140b4d..5795de909609 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -4486,7 +4486,6 @@ static void init_vmcs(struct vcpu_vmx *vmx) static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) { struct vcpu_vmx *vmx = to_vmx(vcpu); - u64 cr0; if (!init_event) init_vmcs(vmx); @@ -4557,9 +4556,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) kvm_make_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu); - cr0 = X86_CR0_NW | X86_CR0_CD | X86_CR0_ET; - vmx->vcpu.arch.cr0 = cr0; - vmx_set_cr0(vcpu, cr0); /* enter rmode */ + vmx_set_cr0(vcpu, X86_CR0_NW | X86_CR0_CD | X86_CR0_ET); vmx_set_cr4(vcpu, 0); vmx_set_efer(vcpu, 0);
Remove a bogus write to vcpu->arch.cr0 that immediately precedes vmx_set_cr0() during vCPU RESET/INIT. For RESET, this is a nop since the "old" CR0 value is meaningless. But for INIT, if the vCPU is coming from paging enabled mode, crushing vcpu->arch.cr0 will cause the various is_paging() checks in vmx_set_cr0() to get false negatives. For the exit_lmode() case, the false negative is benign as vmx_set_efer() is called immediately after vmx_set_cr0(). For EPT without unrestricted guest, the false negative will cause KVM to unnecessarily run with CR3 load/store exiting. But again, this is benign, albeit sub-optimal. Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/kvm/vmx/vmx.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)