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From: "Jan Beulich" <JBeulich@suse.com>
To: George Dunlap <George.Dunlap@eu.citrix.com>, Quan Xu <quan.xu@intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>, Feng Wu <feng.wu@intel.com>,
	Liu Jinsong <jinsong.liu@alibaba-inc.com>,
	DarioFaggioli <dario.faggioli@citrix.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Keir Fraser <keir@xen.org>
Subject: Re: [PATCH 1/2] IOMMU/MMU: Adjust top level functions for VT-d Device-TLB flush error.
Date: Fri, 18 Mar 2016 02:09:53 -0600	[thread overview]
Message-ID: <56EBC5E102000078000DE376@prv-mh.provo.novell.com> (raw)
In-Reply-To: <945CA011AD5F084CBEA3E851C0AB28894B867105@SHSMSX101.ccr.corp.intel.com>

>>> On 18.03.16 at 04:19, <quan.xu@intel.com> wrote:
> On March 17, 2016 8:34pm, George Dunlap <George.Dunlap@eu.citrix.com> wrote:
>> On Thu, Mar 17, 2016 at 12:30 PM, George Dunlap
>> <George.Dunlap@eu.citrix.com> wrote:
>> > On Thu, Mar 17, 2016 at 6:54 AM, Quan Xu <quan.xu@intel.com> wrote:
>> >> --- a/xen/arch/x86/mm/p2m-ept.c
>> >> +++ b/xen/arch/x86/mm/p2m-ept.c
>> >> @@ -830,7 +830,15 @@ out:
>> >>          {
>> >>              if ( iommu_flags )
>> >>                  for ( i = 0; i < (1 << order); i++ )
>> >> -                    iommu_map_page(d, gfn + i, mfn_x(mfn) + i,
>> iommu_flags);
>> >> +                {
>> >> +                    rc = iommu_map_page(d, gfn + i, mfn_x(mfn) + i,
>> iommu_flags);
>> >> +                    if ( rc )
>> >> +                    {
>> >> +                        while ( i-- > 0 )
>> >> +                            iommu_unmap_page(d, gfn + i);
>> >
>> > This won't unmap gfn+0 (since it will break out when i == 0 without
>> > calling unmap).
>> 
>> Oh, no it won't, because the decrement is postfix.
>> 
>> For us mere mortals, I'd appreciate a comment here like this:
>> 
>> /* Postfix operator means we will call unmap with i == 0 */
>> 
> Agreed.
> For these 2 points, to summarize:
>    - adding "unlikely()" to the if() condition, e.g. if ( unlikely(rc) )
>    - adding a comment:
>         /* Postfix operator means we will call unmap with i == 0 */

To be honest, I'm opposed to the addition of such comments.
See also the parallel discussion rooted at
http://lists.xenproject.org/archives/html/xen-devel/2016-03/msg01779.html

Jan


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  reply	other threads:[~2016-03-18  8:09 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-17  6:54 [PATCH 0/2] Check " Quan Xu
2016-03-17  6:54 ` [PATCH 1/2] IOMMU/MMU: Adjust top level functions for " Quan Xu
2016-03-17  7:32   ` Tian, Kevin
2016-03-17  7:58     ` Jan Beulich
2016-03-17  8:00       ` Tian, Kevin
2016-03-17 12:30   ` George Dunlap
2016-03-17 12:33     ` George Dunlap
2016-03-18  3:19       ` Xu, Quan
2016-03-18  8:09         ` Jan Beulich [this message]
2016-03-24  6:45           ` Xu, Quan
2016-03-18  7:54     ` Xu, Quan
2016-03-18  8:19       ` Jan Beulich
2016-03-18  9:09         ` Xu, Quan
2016-03-18  9:29           ` Jan Beulich
2016-03-18  9:38             ` Dario Faggioli
2016-03-18  9:48               ` Jan Beulich
2016-03-21  6:18                 ` Tian, Kevin
2016-03-21 12:22                   ` Jan Beulich
2016-03-24  9:02                 ` Xu, Quan
2016-03-24  9:58                   ` Jan Beulich
2016-03-24 14:12                     ` Xu, Quan
2016-03-24 14:37                       ` Jan Beulich
2016-03-17 17:14   ` Jan Beulich
2016-03-28  3:33     ` Xu, Quan
2016-03-29  7:20       ` Jan Beulich
2016-03-30  2:28         ` Xu, Quan
2016-03-30  2:35           ` Xu, Quan
2016-03-30  8:05           ` Jan Beulich
2016-03-17  6:54 ` [PATCH 2/2] IOMMU/MMU: Adjust low " Quan Xu
2016-03-17  7:37   ` Tian, Kevin
2016-03-18  2:30     ` Xu, Quan
2016-03-18  8:06       ` Jan Beulich
2016-03-21  5:01         ` Tian, Kevin
2016-03-17 15:31   ` George Dunlap
2016-03-18  6:57     ` Xu, Quan
2016-03-18 10:20   ` Jan Beulich
2016-03-25  9:27     ` Xu, Quan
2016-03-29  7:36       ` Jan Beulich
2016-04-11  3:09         ` Xu, Quan
2016-04-11  3:27           ` Xu, Quan
2016-04-11 16:34             ` Jan Beulich
2016-04-12  1:09               ` Xu, Quan

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