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authorAvi Kivity <avi@redhat.com>2012-08-21 16:07:03 +0200
committerMarcelo Tosatti <mtosatti@redhat.com>2012-08-28 01:02:20 +0200
commite2a610d7fc3e285af8061ff071761752255d95f6 (patch)
tree53f141c70dad87f00413bfb42097812270d86096
parentKVM: VMX: Allow real mode emulation using vm86 with dpl=0 (diff)
downloadlinux-e2a610d7fc3e285af8061ff071761752255d95f6.tar.xz
linux-e2a610d7fc3e285af8061ff071761752255d95f6.zip
KVM: VMX: Allow vm86 virtualization of big real mode
Usually, big real mode uses large (4GB) segments. Currently we don't virtualize this; if any segment has a limit other than 0xffff, we emulate. But if we set the vmx-visible limit to 0xffff, we can use vm86 to virtualize real mode; if an access overruns the segment limit, the guest will #GP, which we will trap and forward to the emulator. This results in significantly faster execution, and less risk of hitting an unemulated instruction. If the limit is less than 0xffff, we retain the existing behaviour. Signed-off-by: Avi Kivity <avi@redhat.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
-rw-r--r--arch/x86/kvm/vmx.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 4811d91759a1..fd21eb454663 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3315,7 +3315,7 @@ static bool rmode_segment_valid(struct kvm_vcpu *vcpu, int seg)
if (var.base != (var.selector << 4))
return false;
- if (var.limit != 0xffff)
+ if (var.limit < 0xffff)
return false;
if ((ar | (3 << AR_DPL_SHIFT)) != 0xf3)
return false;