[Xen-devel] [PATCH for-4.7] x86/pv: Correctly fold vIOPL back into vcpu_guest_context

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

c/s f71ecb6 "x86: introduce a new VMASSIST for architectural behaviour of
iopl" shifted the vcpu iopl field by 12, but didn't update the logic which
reconstructs the guests eflags for migration.

Existing guest kernels set a vIOPL of 1, to prevent them from faulting when
accessing IO ports.  This bug manifests as a crash after migrate, as the vIOPL
reverts back to the default of 0, and the guest suffers an unexpected #GP
fault.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 xen/arch/x86/domctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index cba1e37..6e709cb 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -1512,7 +1512,7 @@ void arch_get_info_guest(struct vcpu *v, 
vcpu_guest_context_u c)
 
         /* IOPL privileges are virtualised: merge back into returned eflags. */
         BUG_ON((c(user_regs.eflags) & X86_EFLAGS_IOPL) != 0);
-        c(user_regs.eflags |= v->arch.pv_vcpu.iopl << 12);
+        c(user_regs.eflags |= v->arch.pv_vcpu.iopl);
 
         if ( !compat )
         {
-- 
2.1.4


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel