From: Avi Kivity <avi@qumranet.com>
Date: Tue, 20 Mar 2007 16:40:40 +0000 (+0200)
Subject: KVM: Workaround vmx inability to virtualize the reset state
X-Git-Tag: v2.6.22-rc1~1008^2~43
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8cb5b0333250beb382624f626851a31f601b4830;p=linux-2.6

KVM: Workaround vmx inability to virtualize the reset state

The reset state has cs.selector == 0xf000 and cs.base == 0xffff0000,
which aren't compatible with vm86 mode, which is used for real mode
virtualization.

When we create a vcpu, we set cs.base to 0xf0000, but if we get there by
way of a reset, the values are inconsistent and vmx refuses to enter
guest mode.

Workaround by detecting the state and munging it appropriately.

Signed-off-by: Avi Kivity <avi@qumranet.com>
---

diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 0d9bf0b36d..aa7e2ba6fb 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -712,6 +712,8 @@ static void enter_rmode(struct kvm_vcpu *vcpu)
 
 	vmcs_write32(GUEST_CS_AR_BYTES, 0xf3);
 	vmcs_write32(GUEST_CS_LIMIT, 0xffff);
+	if (vmcs_readl(GUEST_CS_BASE) == 0xffff0000)
+		vmcs_writel(GUEST_CS_BASE, 0xf0000);
 	vmcs_write16(GUEST_CS_SELECTOR, vmcs_readl(GUEST_CS_BASE) >> 4);
 
 	fix_rmode_seg(VCPU_SREG_ES, &vcpu->rmode.es);