From e2a610d7fc3e285af8061ff071761752255d95f6 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Tue, 21 Aug 2012 17:07:03 +0300 Subject: [PATCH] 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 Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/vmx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 4811d91..fd21eb4 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; -- 2.7.4