From: "H. Peter Anvin" <hpa@zytor.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
Xen-devel <xen-devel@lists.xen.org>
Cc: David Vrabel <david.vrabel@citrix.com>,
Rusty Russell <rusty@rustcorp.com.au>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
lguest@lists.ozlabs.org, stable@vger.kernel.org
Subject: Re: [PATCH] x86/cpu: Fix SMAP check in PVOPS environments
Date: Wed, 03 Jun 2015 23:38:40 -0700 [thread overview]
Message-ID: <556FF270.5060306@zytor.com> (raw)
In-Reply-To: <1433323874-6927-1-git-send-email-andrew.cooper3@citrix.com>
On 06/03/2015 02:31 AM, Andrew Cooper wrote:
> There appears to be no formal statement of what pv_irq_ops.save_fl() is
> supposed to return precisely. Native returns the full flags, while lguest and
> Xen only return the Interrupt Flag, and both have comments by the
> implementations stating that only the Interrupt Flag is looked at. This may
> have been true when initially implemented, but no longer is.
>
> To make matters worse, the Xen PVOP leaves the upper bits undefined, making
> the BUG_ON() undefined behaviour. Experimentally, this now trips for 32bit PV
> guests on Broadwell hardware. The BUG_ON() is consistent for an individual
> build, but not consistent for all builds. It has also been a sitting timebomb
> since SMAP support was introduced.
>
> Use native_save_fl() instead, which will obtain an accurate view of the AC
> flag.
Could we fix the Xen pvops wrapper instead to not do things like this?
-hpa
next prev parent reply other threads:[~2015-06-04 6:39 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-03 9:31 [PATCH] x86/cpu: Fix SMAP check in PVOPS environments Andrew Cooper
2015-06-04 6:38 ` H. Peter Anvin [this message]
2015-06-04 8:58 ` Andrew Cooper
2015-06-04 19:55 ` Rusty Russell
2015-06-04 20:29 ` H. Peter Anvin
2015-06-05 2:58 ` Rusty Russell
2015-06-05 7:13 ` Ingo Molnar
2015-06-05 9:33 ` [Xen-devel] " David Vrabel
2015-11-17 14:59 ` Andrew Cooper
2015-11-19 10:12 ` [tip:x86/urgent] " tip-bot for Andrew Cooper
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