From: Avi Kivity Date: Tue, 21 Aug 2012 14:07:03 +0000 (+0300) Subject: KVM: VMX: Allow vm86 virtualization of big real mode X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=e2a610d7fc3e285af8061ff071761752255d95f6;p=linux-beck.git 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 --- 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;