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authorPaolo Bonzini <pbonzini@redhat.com>2015-12-22 15:20:00 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2015-12-22 15:29:00 +0100
commite24dea2afc6a0852983dc741072d8e96155e13f5 (patch)
tree80b972cf9cd865559d6b6aae01392bc5bc4321b3
parentfa7c4ebd5ae0c22f9908436303106a9ffcf0cf42 (diff)
downloadlinux-stericsson-e24dea2afc6a0852983dc741072d8e96155e13f5.tar.gz
KVM: MTRR: treat memory as writeback if MTRR is disabled in guest CPUID
Virtual machines can be run with CPUID such that there are no MTRRs. In that case, the firmware will never enable MTRRs and it is obviously undesirable to run the guest entirely with UC memory. Check out guest CPUID, and use WB memory if MTRR do not exist. Cc: qemu-stable@nongnu.org Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=107561 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--arch/x86/kvm/cpuid.h8
-rw-r--r--arch/x86/kvm/mtrr.c14
2 files changed, 19 insertions, 3 deletions
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 06332cb7e7d1..3f5c48ddba45 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -38,6 +38,14 @@ static inline bool guest_cpuid_has_xsave(struct kvm_vcpu *vcpu)
return best && (best->ecx & bit(X86_FEATURE_XSAVE));
}
+static inline bool guest_cpuid_has_mtrr(struct kvm_vcpu *vcpu)
+{
+ struct kvm_cpuid_entry2 *best;
+
+ best = kvm_find_cpuid_entry(vcpu, 1, 0);
+ return best && (best->edx & bit(X86_FEATURE_MTRR));
+}
+
static inline bool guest_cpuid_has_tsc_adjust(struct kvm_vcpu *vcpu)
{
struct kvm_cpuid_entry2 *best;
diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
index 7747b6d716fa..3f8c732117ec 100644
--- a/arch/x86/kvm/mtrr.c
+++ b/arch/x86/kvm/mtrr.c
@@ -120,14 +120,22 @@ static u8 mtrr_default_type(struct kvm_mtrr *mtrr_state)
return mtrr_state->deftype & IA32_MTRR_DEF_TYPE_TYPE_MASK;
}
-static u8 mtrr_disabled_type(void)
+static u8 mtrr_disabled_type(struct kvm_vcpu *vcpu)
{
/*
* Intel SDM 11.11.2.2: all MTRRs are disabled when
* IA32_MTRR_DEF_TYPE.E bit is cleared, and the UC
* memory type is applied to all of physical memory.
+ *
+ * However, virtual machines can be run with CPUID such that
+ * there are no MTRRs. In that case, the firmware will never
+ * enable MTRRs and it is obviously undesirable to run the
+ * guest entirely with UC memory and we use WB.
*/
- return MTRR_TYPE_UNCACHABLE;
+ if (guest_cpuid_has_mtrr(vcpu))
+ return MTRR_TYPE_UNCACHABLE;
+ else
+ return MTRR_TYPE_WRBACK;
}
/*
@@ -675,7 +683,7 @@ u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn)
}
if (iter.mtrr_disabled)
- return mtrr_disabled_type();
+ return mtrr_disabled_type(vcpu);
/* not contained in any MTRRs. */
if (type == -1)