Subject: Re: [Xen-devel] [PATCH v3 4/4] x86/asm: Rewrite sync_core() to use
 IRET-to-self
To: Jan Beulich <JBeulich@suse.com>, Andy Lutomirski <luto@kernel.org>
References: <cover.1480973468.git.luto@kernel.org>
 <cover.1480973468.git.luto@kernel.org>
 <c452beb3aaa5a0232b5ef27f443f0c27b6c65fe2.1480973468.git.luto@kernel.org>
 <584688FD02000078001257BB@prv-mh.provo.novell.com>
Cc: Borislav Petkov <bp@alien8.de>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        Brian Gerst <brgerst@gmail.com>,
        Matthew Whitehead <tedheadster@gmail.com>,
        Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        xen-devel <Xen-devel@lists.xen.org>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <JGross@suse.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
From: "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <32e056b6-378f-a461-dfcd-442b582763a9@zytor.com>
Date: Tue, 6 Dec 2016 11:32:00 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101
 Thunderbird/45.4.0
MIME-Version: 1.0
In-Reply-To: <584688FD02000078001257BB@prv-mh.provo.novell.com>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 504
Lines: 21

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