From: "H. Peter Anvin" <hpa@zytor.com>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Chuck Ebbert <cebbert@redhat.com>,
Arjan van de Ven <arjan@infradead.org>,
Kirill Korotaev <dev@openvz.org>, Andrew Morton <akpm@osdl.org>,
Andi Kleen <ak@suse.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
devel@openvz.org
Subject: Re: [PATCH] mark read_crX() asm code as volatile
Date: Tue, 02 Oct 2007 23:18:22 -0700 [thread overview]
Message-ID: <4703342E.3020101@zytor.com> (raw)
In-Reply-To: <200710022214.55381.nickpiggin@yahoo.com.au>
Nick Piggin wrote:
>>
>> This should work because the result gets used before reading again:
>>
>> read_cr3(a);
>> write_cr3(a | 1);
>> read_cr3(a);
>>
>> But this might be reordered so that b gets read before the write:
>>
>> read_cr3(a);
>> write_cr3(a | 1);
>> read_cr3(b);
>>
>> ?
>
> I don't see how, as write_cr3 clobbers memory.
Because read_cr3() doesn't depend on memory, and b could be stored in a
register.
-hpa
next prev parent reply other threads:[~2007-10-03 6:22 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-02 14:08 [PATCH] mark read_crX() asm code as volatile Kirill Korotaev
2007-10-02 14:17 ` Andi Kleen
2007-10-02 15:28 ` Arjan van de Ven
2007-10-02 18:27 ` Chuck Ebbert
2007-10-02 12:14 ` Nick Piggin
2007-10-03 6:18 ` H. Peter Anvin [this message]
2007-10-02 15:49 ` Nick Piggin
2007-10-03 8:45 ` Andi Kleen
2007-10-02 19:21 ` H. Peter Anvin
2007-10-03 8:25 ` Kirill Korotaev
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