4.2-stable review patch. If anyone has any objections, please let me know.
------------------
From: Paolo Bonzini <pbonz...@redhat.com>
commit 606decd67049217684e3cb5a54104d51ddd4ef35 upstream.
This reverts commit fd717f11015f673487ffc826e59b2bad69d20fe5.
It was reported to cause Machine Check Exceptions (bug 104091).
Reported-by: harn-s...@gmx.de
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
arch/x86/kvm/svm.c | 7 +++++--
arch/x86/kvm/vmx.c | 11 ++++++++---
2 files changed, 13 insertions(+), 5 deletions(-)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1166,11 +1166,14 @@ static u64 svm_get_mt_mask(struct kvm_vc
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;
mtrr = kvm_mtrr_get_guest_memory_type(vcpu, gfn);
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -8634,17 +8634,22 @@ static u64 vmx_get_mt_mask(struct kvm_vc
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;
--
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