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Commit fd717f11 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

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



Currently guest MTRR is avoided if kvm_is_reserved_pfn returns true.
However, the guest could prefer a different page type than UC for
such pages. A good example is that pass-throughed VGA frame buffer is
not always UC as host expected.

This patch enables full use of virtual guest MTRRs.

Suggested-by: default avatarXiao Guangrong <guangrong.xiao@linux.intel.com>
Tested-by: Joerg Roedel <jroedel@suse.de> (on AMD)
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent e098223b

arch/x86/kvm/svm.c

+2 −5
Original line number Diff line number Diff line
@@ -1166,14 +1166,11 @@ static u64 svm_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) 
	u8 mtrr;



	/*

	 * 1. MMIO: always map as UC

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

	 * 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)

		return _PAGE_NOCACHE;



	if (!kvm_arch_has_assigned_device(vcpu->kvm))

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

		return 0;



	mtrr = kvm_mtrr_get_guest_memory_type(vcpu, gfn);

arch/x86/kvm/vmx.c

+3 −8
Original line number Diff line number Diff line
@@ -8632,22 +8632,17 @@ 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: always map as UC

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

	 * 2. EPT with VT-d:

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

	 *	result, try to trust guest.

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

	 *   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) {

		cache = MTRR_TYPE_UNCACHABLE;

		goto exit;

	}



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

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

		ipat = VMX_EPT_IPAT_BIT;

		cache = MTRR_TYPE_WRBACK;

		goto exit;