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From: Paolo Bonzini <pbonzini@redhat.com>
To: Borislav Petkov <bp@suse.de>
Cc: Minfei Huang <mnghuan@gmail.com>,
	luto@kernel.org, hpa@zytor.com, mingo@redhat.com,
	tglx@linutronix.de, x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3 V2] pvclock: Get rid of __pvclock_read_cycles in function pvclock_read_flags
Date: Thu, 9 Jun 2016 14:31:15 +0200	[thread overview]
Message-ID: <17556f35-2c69-4793-27bf-3280f0177122@redhat.com> (raw)
In-Reply-To: <20160609112807.GB12860@pd.tnic>



On 09/06/2016 13:28, Borislav Petkov wrote:
>> > technically, they should be virt_rmb() -- it really doesn't matter of
>> > course because reads are never reordered on x86.
> You mean
> 
> 	version = src->version;
> 	flags = src->flags;
> 
> are not reordered?
> 
> I don't think so.

The compiler can reorder them, so smp_rmb() and virt_rmb() have to be
barrier(), but the processor won't.

x86 will only move a store after a subsequent load, if you exclude
special cases such as write combining, non-temporal moves and the like.
LFENCE and SFENCE are only needed for those special cases.

Paolo

  reply	other threads:[~2016-06-09 12:31 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-27  6:17 [PATCH 1/3] pvclock: Add CPU barries to get correct version value Minfei Huang
2016-05-27  6:17 ` [PATCH 2/3] pvclock: Cleanup to remove function pvclock_get_nsec_offset Minfei Huang
2016-05-27 15:40   ` Andy Lutomirski
2016-05-27  6:17 ` [PATCH 3/3] pvclock: Add a new wrapper function to only get variable flags Minfei Huang
2016-05-27 15:40   ` Andy Lutomirski
2016-05-27 16:06     ` Paolo Bonzini
2016-05-28 12:02       ` Minfei Huang
2016-05-28 12:27   ` [PATCH 3/3 V2] pvclock: Get rid of __pvclock_read_cycles in function pvclock_read_flags Minfei Huang
2016-06-07 13:16     ` Minfei Huang
2016-06-09 11:17       ` Paolo Bonzini
2016-06-08  8:17     ` Borislav Petkov
2016-06-09 11:21       ` Paolo Bonzini
2016-06-09 11:28         ` Borislav Petkov
2016-06-09 12:31           ` Paolo Bonzini [this message]
2016-06-12 11:46           ` Minfei Huang
2016-06-09 12:16     ` Peter Zijlstra
2016-06-09 12:24       ` Peter Zijlstra
2016-06-09 12:26       ` Paolo Bonzini
2016-06-09 12:35         ` Peter Zijlstra
2016-05-27 15:39 ` [PATCH 1/3] pvclock: Add CPU barries to get correct version value Andy Lutomirski

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