linux-kernel - Re: [Xen-devel] [PATCH v3 4/4] x86/asm: Rewrite sync

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Message-ID: <32e056b6-378f-a461-dfcd-442b582763a9@zytor.com>
Date:   Tue, 6 Dec 2016 11:32:00 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Jan Beulich <JBeulich@...e.com>, Andy Lutomirski <luto@...nel.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Brian Gerst <brgerst@...il.com>,
        Matthew Whitehead <tedheadster@...il.com>,
        Henrique de Moraes Holschuh <hmh@....eng.br>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        xen-devel <Xen-devel@...ts.xen.org>,
        One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <JGross@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH v3 4/4] x86/asm: Rewrite sync_core() to use
 IRET-to-self

On 12/06/16 00:46, Jan Beulich wrote:
>> +
>> +#ifdef CONFIG_X86_32
>> +	asm volatile (
>> +		"pushfl\n\t"
>> +		"pushl %%cs\n\t"
>> +		"pushl $1f\n\t"
>> +		"iret\n\t"
>> +		"1:"
>> +		: "+r" (__sp) : : "cc", "memory");
> 
> I don't thing EFLAGS (i.e. "cc") gets modified anywhere here. And
> the memory clobber would perhaps better be pulled out into an
> explicit barrier() invocation (making it more obvious what it's needed
> for)?
> 

Not to mention "cc" doesn't do anything on x86 at all.

	-hpa