linux-kernel - Re: [PATCH] xen/x86: Adjust stack pointer in xen

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Message-ID: <20151116195906.GB20137@pd.tnic>
Date:	Mon, 16 Nov 2015 20:59:06 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	xen-devel <xen-devel@...ts.xen.org>,
	David Vrabel <david.vrabel@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH] xen/x86: Adjust stack pointer in xen_sysexit

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.

ECO tip #101: Trim your mails when you reply.
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