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: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Tested-by: Joerg Roedel <jroedel@suse.de> (on AMD)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index d36cfaf..bbc678a 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1166,14 +1166,11 @@
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);