From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
Xen-devel <xen-devel@lists.xen.org>
Cc: Wei Liu <wei.liu2@citrix.com>, Jan Beulich <JBeulich@suse.com>
Subject: Re: [PATCH for-4.7] x86/pv: Correctly fold vIOPL back into vcpu_guest_context
Date: Mon, 11 Apr 2016 10:08:58 -0400 [thread overview]
Message-ID: <570BAFFA.5010406@oracle.com> (raw)
In-Reply-To: <1460365435-12325-1-git-send-email-andrew.cooper3@citrix.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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next prev parent reply other threads:[~2016-04-11 14:08 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-11 9:03 [PATCH for-4.7] x86/pv: Correctly fold vIOPL back into vcpu_guest_context Andrew Cooper
2016-04-11 9:45 ` Wei Liu
2016-04-11 14:08 ` Boris Ostrovsky [this message]
2016-04-11 14:22 ` Konrad Rzeszutek Wilk
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