linux-kernel - RE: [PATCH] iommu/vt-d: Use cmpxchg16b to update posted format IRTE atomically

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Message-ID: <E959C4978C3B6342920538CF579893F00ADDD81E@SHSMSX104.ccr.corp.intel.com>
Date:	Fri, 16 Oct 2015 01:01:02 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	Joerg Roedel <joro@...tes.org>
CC:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [PATCH] iommu/vt-d: Use cmpxchg16b to update posted format IRTE
 atomically



> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
> owner@...r.kernel.org] On Behalf Of Joerg Roedel
> Sent: Thursday, October 15, 2015 10:24 PM
> To: Wu, Feng <feng.wu@...el.com>
> Cc: iommu@...ts.linux-foundation.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] iommu/vt-d: Use cmpxchg16b to update posted format
> IRTE atomically
> 
> On Thu, Oct 15, 2015 at 10:19:11AM +0800, Feng Wu wrote:
> > If IRTE is in posted format, the 'pda' field goes across the 64-bit
> > boundary, we need use cmpxchg16b to atomically update it. We only
> > expose posted-interrupt when X86_FEATURE_CX16 is supported and use
> > to update it atomically.
> > +
> > +		ret = cmpxchg_double(&irte->low, &irte->high,
> > +				     irte->low, irte->high,
> > +				     irte_modified->low, irte_modified->high);
> > +		/*
> > +		 * We use cmpxchg16 to atomically update the 128-bit IRTE,
> > +		 * and it cannot be updated by the hardware or other
> processors
> > +		 * behind us, so the return value of cmpxchg16 should be the
> > +		 * same as the old value.
> > +		 */
> > +		BUG_ON(!ret);
> 
> Changed this to a WARN_ON, otherwise applied.

Thanks a lot, Joerg!

Thanks,
Feng
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