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Commit 606decd6 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

Revert "KVM: x86: apply guest MTRR virtualization on host reserved pages" 



This reverts commit fd717f11.
It was reported to cause Machine Check Exceptions (bug 104091).

Reported-by: default avatar <harn-solo@gmx.de>
Cc: stable@vger.kernel.org # 4.2+
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 9bac175d

arch/x86/kvm/svm.c

+5 −2
Original line number Diff line number Diff line
@@ -1167,11 +1167,14 @@ static u64 svm_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) 
	u8 mtrr;



	/*

	 * 1. MMIO: trust guest MTRR, so same as item 3.

	 * 1. MMIO: always map as UC

	 * 2. No passthrough: always map as WB, and force guest PAT to WB as well

	 * 3. Passthrough: can't guarantee the result, try to trust guest.

	 */

	if (!is_mmio && !kvm_arch_has_assigned_device(vcpu->kvm))

	if (is_mmio)

		return _PAGE_NOCACHE;



	if (!kvm_arch_has_assigned_device(vcpu->kvm))

		return 0;



	if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED) &&

arch/x86/kvm/vmx.c

+8 −3
Original line number Diff line number Diff line
@@ -8617,17 +8617,22 @@ static u64 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) 
	u64 ipat = 0;



	/* For VT-d and EPT combination

	 * 1. MMIO: guest may want to apply WC, trust it.

	 * 1. MMIO: always map as UC

	 * 2. EPT with VT-d:

	 *   a. VT-d without snooping control feature: can't guarantee the

	 *	result, try to trust guest.  So the same as item 1.

	 *	result, try to trust guest.

	 *   b. VT-d with snooping control feature: snooping control feature of

	 *	VT-d engine can guarantee the cache correctness. Just set it

	 *	to WB to keep consistent with host. So the same as item 3.

	 * 3. EPT without VT-d: always map as WB and set IPAT=1 to keep

	 *    consistent with host MTRR

	 */

	if (!is_mmio && !kvm_arch_has_noncoherent_dma(vcpu->kvm)) {

	if (is_mmio) {

		cache = MTRR_TYPE_UNCACHABLE;

		goto exit;

	}



	if (!kvm_arch_has_noncoherent_dma(vcpu->kvm)) {

		ipat = VMX_EPT_IPAT_BIT;

		cache = MTRR_TYPE_WRBACK;

		goto exit;