linux-kernel - Re: [PATCH 1/3] x86/xen: Avoid fast syscall path for Xen PV guests

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Message-ID: <20151119120809.GC5953@pd.tnic>
Date:	Thu, 19 Nov 2015 13:08:09 +0100
From:	Borislav Petkov <bp@...e.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andrew Lutomirski <luto@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 1/3] x86/xen: Avoid fast syscall path for Xen PV guests

On Wed, Nov 18, 2015 at 12:21:56PM -0800, Andy Lutomirski wrote:
> Could we make this a little less subtle:
> 
> ALTERNATIVE "testl %eax, %eax; lz .Lsyscall_32_done", "jmp
> .Lsyscasll_32_done", X86_FEATURE_XENPV
> 
> Borislav, what do you think?

I don't mind either.

I would've said your version doesn't touch %eax so the result in there
might be useful for callers but all paths do overwrite it, AFAICT.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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