Re: [PATCH] xen/x86: Adjust stack pointer in xen_sysexit

From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	David Vrabel <david.vrabel@citrix.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH] xen/x86: Adjust stack pointer in xen_sysexit
Date: Mon, 16 Nov 2015 20:59:06 +0100	[thread overview]
Message-ID: <20151116195906.GB20137__46970.7302669578$1447704045$gmane$org@pd.tnic> (raw)
In-Reply-To: <CALCETrUc+dbVY4JRUOqTCZpXndz7OJkchMU7nfc8QNyjgRxY2w@mail.gmail.com>

On Mon, Nov 16, 2015 at 11:03:22AM -0800, Andy Lutomirski wrote:

> ...
> The reader surely doesn't remember that this isn't guaranteed to be a
> swapgs instruction on native.  Using:
> 
> ALTERNATIVE "swapgs" "" X86_FEATURE_XENPV
> 
> would be safer (it would get rid of the SWAPGS_UNSAFE_STACK mess) and
> much clearer.  We could hide *that* behind a macro and no one would be
> confused.  (Well, they'd be confused by the fact that Xen PV handles
> gsbase very differently from native, but that has nothing to do with
> the macro.)
> 
> I think we could convert piecemeal, and I wonder if this new patch for
> 32-bit native on 4.4 (this is needed for 4.4, right?) would be a good
> starting point.  Borislav, what do you think?  Would you be okay with
> adding a Xen PV pseudofeature?

AFAICT, I'd prefer this becomes rather a jump label which gets enabled
on xen. Especially if a single pseudofeature might not be enough,
apprently...

-- 
Regards/Gruss,
    Boris.

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