[PATCH UNTESTED] KVM: VMX: Save/restore rflags.vm correctly in real mode

[PATCH UNTESTED] KVM: VMX: Save/restore rflags.vm correctly in real mode

[Avi Kivity]

Currently we set eflags.vm unconditionally when entering real mode emulation
through virtual-8086 mode, and clear it unconditionally when we enter protected
mode.  The means that the following sequence

  KVM_SET_REGS  (rflags.vm=1)
  KVM_SET_SREGS (cr0.pe=1)

Ends up with rflags.vm clear due to KVM_SET_SREGS triggering enter_pmode().

Fix by shadowing rflags.vm (and rflags.iopl) correctly while in real mode:
reads and writes to those bits access a shadow register instead of the actual
register.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 arch/x86/kvm/vmx.c |   24 +++++++++++++++---------
 1 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 41e63bb..2bd30b9 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -76,6 +76,8 @@ module_param(emulate_invalid_guest_state, bool, S_IRUGO);
 #define KVM_PMODE_VM_CR4_ALWAYS_ON (X86_CR4_PAE | X86_CR4_VMXE)
 #define KVM_RMODE_VM_CR4_ALWAYS_ON (X86_CR4_VME | X86_CR4_PAE | X86_CR4_VMXE)
 
+#define RMODE_GUEST_OWNED_EFLAGS_BITS (~(X86_EFLAGS_IOPL | X86_EFLAGS_VM))
+
 /*
  * These 2 parameters are used to config the controls for Pause-Loop Exiting:
  * ple_gap:    upper bound on the amount of time between two successive
@@ -130,7 +132,7 @@ struct vcpu_vmx {
 	} host_state;
 	struct {
 		int vm86_active;
-		u8 save_iopl;
+		ulong save_rflags;
 		struct kvm_save_segment {
 			u16 selector;
 			unsigned long base;
@@ -854,18 +856,23 @@ static void vmx_fpu_deactivate(struct kvm_vcpu *vcpu)
 
 static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
 {
-	unsigned long rflags;
+	unsigned long rflags, save_rflags;
 
 	rflags = vmcs_readl(GUEST_RFLAGS);
-	if (to_vmx(vcpu)->rmode.vm86_active)
-		rflags &= ~(unsigned long)(X86_EFLAGS_IOPL | X86_EFLAGS_VM);
+	if (to_vmx(vcpu)->rmode.vm86_active) {
+		rflags &= RMODE_GUEST_OWNED_EFLAGS_BITS;
+		save_rflags = to_vmx(vcpu)->rmode.save_rflags;
+		rflags |= save_rflags & ~RMODE_GUEST_OWNED_EFLAGS_BITS;
+	}
 	return rflags;
 }
 
 static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
 {
-	if (to_vmx(vcpu)->rmode.vm86_active)
+	if (to_vmx(vcpu)->rmode.vm86_active) {
+		to_vmx(vcpu)->rmode.save_rflags = rflags;
 		rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
+	}
 	vmcs_writel(GUEST_RFLAGS, rflags);
 }
 
@@ -1519,8 +1526,8 @@ static void enter_pmode(struct kvm_vcpu *vcpu)
 	vmcs_write32(GUEST_TR_AR_BYTES, vmx->rmode.tr.ar);
 
 	flags = vmcs_readl(GUEST_RFLAGS);
-	flags &= ~(X86_EFLAGS_IOPL | X86_EFLAGS_VM);
-	flags |= (vmx->rmode.save_iopl << IOPL_SHIFT);
+	flags &= RMODE_GUEST_OWNED_EFLAGS_BITS;
+	flags |= vmx->rmode.save_rflags & ~RMODE_GUEST_OWNED_EFLAGS_BITS;
 	vmcs_writel(GUEST_RFLAGS, flags);
 
 	vmcs_writel(GUEST_CR4, (vmcs_readl(GUEST_CR4) & ~X86_CR4_VME) |
@@ -1593,8 +1600,7 @@ static void enter_rmode(struct kvm_vcpu *vcpu)
 	vmcs_write32(GUEST_TR_AR_BYTES, 0x008b);
 
 	flags = vmcs_readl(GUEST_RFLAGS);
-	vmx->rmode.save_iopl
-		= (flags & X86_EFLAGS_IOPL) >> IOPL_SHIFT;
+	vmx->rmode.save_rflags = flags;
 
 	flags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
 
-- 
1.7.0.4

Re: [PATCH UNTESTED] KVM: VMX: Save/restore rflags.vm correctly in real mode

[Marcelo Tosatti]

On Thu, Apr 08, 2010 at 06:19:35PM +0300, Avi Kivity wrote:
> Currently we set eflags.vm unconditionally when entering real mode emulation
> through virtual-8086 mode, and clear it unconditionally when we enter protected
> mode.  The means that the following sequence
> 
>   KVM_SET_REGS  (rflags.vm=1)
>   KVM_SET_SREGS (cr0.pe=1)
> 
> Ends up with rflags.vm clear due to KVM_SET_SREGS triggering enter_pmode().
> 
> Fix by shadowing rflags.vm (and rflags.iopl) correctly while in real mode:
> reads and writes to those bits access a shadow register instead of the actual
> register.
> 
> Signed-off-by: Avi Kivity <avi@redhat.com>

Tested and applied, thanks.