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KVM: svm: handle KVM_X86_QUIRK_CD_NW_CLEARED in svm_get_mt_mask

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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
microcode, where CD/NW are not touched by vmentry/vmexit.  However,
keep this dependent on the quirk because OVMF enables the caches
too late.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2015-07-10 13:32:13 +02:00
parent 5f3d45e7f2
commit 5492830370
1 changed files with 8 additions and 7 deletions
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15
arch/x86/kvm/svm.c
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@ -1173,6 +1173,10 @@ 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_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED) &&
kvm_read_cr0(vcpu) & X86_CR0_CD)
return _PAGE_NOCACHE;
mtrr = kvm_mtrr_get_guest_memory_type(vcpu, gfn);
return mtrr2protval[mtrr];
}
@ -1667,13 +1671,10 @@ 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 (kvm_check_has_quirk(vcpu->kvm, KVM_X86_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);