On Mon, Apr 11, 2016 at 10:03:55AM +0100, Andrew Cooper wrote:
> 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.coop...@citrix.com>
> ---
> CC: Jan Beulich <jbeul...@suse.com>
> CC: Wei Liu <wei.l...@citrix.com>
FWIW:
Reviewed-by: Wei Liu <wei.l...@citrix.com>
This is fine for 4.7.
Wei.
> ---
> 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
>
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