We can disable CD unconditionally when there is no assigned device. KVM now forces guest PAT to all-writeback in that case, so it makes sense to also force CR0.CD=0. When there are assigned devices, emulate cache-disabled operation through the page tables. This behavior is consistent with VMX, where CD/NW are not touched by vmentry/vmexit. Note that buggy firmware that does not clear CD/NW is _seriously_ old: SeaBIOS for example has been doing it since October 2008. Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> --- arch/x86/kvm/svm.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index bbc678a66b18..9b1513065a6a 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -1173,6 +1173,9 @@ static u64 svm_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) if (!is_mmio && !kvm_arch_has_assigned_device(vcpu->kvm)) return 0; + if (kvm_read_cr0(vcpu) & X86_CR0_CD) + return _PAGE_NOCACHE; + mtrr = kvm_mtrr_get_guest_memory_type(vcpu, gfn); return mtrr2protval[mtrr]; } @@ -1667,13 +1670,10 @@ static void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0) if (!vcpu->fpu_active) cr0 |= X86_CR0_TS; - /* - * re-enable caching here because the QEMU bios - * does not do it - this results in some delay at - * reboot - */ - if (!(vcpu->kvm->arch.disabled_quirks & KVM_QUIRK_CD_NW_CLEARED)) - cr0 &= ~(X86_CR0_CD | X86_CR0_NW); + + /* These are emulated via page tables. */ + cr0 &= ~(X86_CR0_CD | X86_CR0_NW); + svm->vmcb->save.cr0 = cr0; mark_dirty(svm->vmcb, VMCB_CR); update_cr0_intercept(svm); -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
