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

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 04/11/2016 05:03 AM, 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.cooper3@citrix.com>

Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

(save/restore was part of brokenness as well, obviously)

> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Wei Liu <wei.liu2@citrix.com>
> ---
>   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 )
>           {


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