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

[Wu, Feng]

> -----Original Message-----
> From: linux-kernel-owner@xxxxxxxxxxxxxxx [mailto:linux-kernel-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Joerg Roedel
> Sent: Thursday, October 15, 2015 10:24 PM
> To: Wu, Feng <feng.wu@xxxxxxxxx>
> Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> 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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