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From: "Tian, Kevin" <kevin.tian@intel.com>
To: "Xu, Quan" <quan.xu@intel.com>, Jan Beulich <JBeulich@suse.com>
Cc: "andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
	"dario.faggioli@citrix.com" <dario.faggioli@citrix.com>,
	"keir@xen.org" <keir@xen.org>, "Wu, Feng" <feng.wu@intel.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [PATCH v8 09/11] vt-d: fix the IOMMU flush issue
Date: Wed, 15 Jun 2016 01:42:18 +0000	[thread overview]
Message-ID: <AADFC41AFE54684AB9EE6CBC0274A5D15F8B5367@SHSMSX103.ccr.corp.intel.com> (raw)
In-Reply-To: <945CA011AD5F084CBEA3E851C0AB28894B8E5352@SHSMSX103.ccr.corp.intel.com>

> From: Xu, Quan
> Sent: Tuesday, June 14, 2016 5:04 PM
> 
> On June 14, 2016 4:27 PM, Jan Beulich <JBeulich@suse.com> wrote:
> > >>> On 14.06.16 at 10:10, <quan.xu@intel.com> wrote:
> > > On June 13, 2016 11:52 PM, Jan Beulich <jbeulich@suse.com> wrote:
> > >> >>> "Xu, Quan" <quan.xu@intel.com> 06/13/16 5:22 PM >>>
> > >> >From: Quan Xu <quan.xu@intel.com>
> > >> >@@ -546,17 +550,37 @@ static int __must_check iommu_flush_all(void)
> > >> >struct acpi_drhd_unit *drhd; struct iommu *iommu; int
> > >> >flush_dev_iotlb;
> > >> >+    int rc = 0;
> > >>  >
> > >> >flush_all_cache();
> > >> >for_each_drhd_unit ( drhd )
> > >> >{
> > >> >+        int iommu_rc, iommu_ret;
> > >> >+
> > >> >iommu = drhd->iommu;
> > >> >-        iommu_flush_context_global(iommu, 0);
> > >> >+        iommu_rc = iommu_flush_context_global(iommu, 0);
> > >> >flush_dev_iotlb = find_ats_dev_drhd(iommu) ? 1 : 0;
> > >> >-        iommu_flush_iotlb_global(iommu, 0, flush_dev_iotlb);
> > >> >+        iommu_ret = iommu_flush_iotlb_global(iommu, 0,
> > >> >+ flush_dev_iotlb);
> > >> >+
> > >> >+        /*
> > >> >+         * The current logic for returns:
> > >> >+         *   - positive  invoke iommu_flush_write_buffer to flush cache.
> > >> >+         *   - zero      on success.
> > >> >+         *   - negative  on failure. Continue to flush IOMMU IOTLB on a
> > >> >+         *               best effort basis.
> > >> >+         */
> > >> >+        if ( iommu_rc > 0 || iommu_ret > 0 )
> > >> >+            iommu_flush_write_buffer(iommu);
> > >> >+        if ( rc >= 0 )
> > >> >+            rc = iommu_rc;
> > >> >+        if ( rc >= 0 )
> > >> >+            rc = iommu_ret;
> > >>
> > >> First of all - is it correct to fold the two
> > >> iommu_flush_write_buffer() invocations?
> > >>
> > >
> > > Sure, it is correct..
> > >
> > > as:
> > > - For updates to remapping hardware structures that require
> > > context-cache, PASID-cache, IOTLB or IEC invalidation Operations to
> > > flush stale entries from the hardware caches, no additional action is
> > > required to make the modification Visible to hardware. This is
> > > because, hardware performs an implicit write-buffer-flushing as a
> > > pre-condition to context-cache, PASID-cache, IOTLB and IEC
> > > invalidation operations.
> > >
> > > - For updates to remapping hardware structures (such as modifying a
> > > currently not-present entry) that do not require Context-cache, IOTLB,
> > > or IEC invalidations, software must explicitly perform
> > > write-buffer-flushing to ensure the updated structures Are visible to
> > > hardware.
> >
> > But that's not the point. Instead my question was related to Kevin's concern
> > towards you making assumptions on the behavior of
> > iommu_flush_context_global() vs iommu_flush_iotlb_global(): What if the
> > first returned 1 but the second didn't?
> > It would seem to me that in such a
> > (theoretical) case iommu_flush_write_buffer() might need to be invoked prior
> > to the second flush function.
> 
> In this case, it is correct too.
> As , hardware performs an __implicit__ write-buffer-flushing as a __pre-condition__ to
> IOTLB invalidation operation.
> So software is no need to call iommu_flush_write_buffer() to explicitly perform
> write-buffer-flushing for that the first returned 1.
> 

Yes, there is no issue doing so based on spec.

Thanks
Kevin

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  reply	other threads:[~2016-06-15  1:42 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-13 15:17 [PATCH v8 00/11] Check VT-d Device-TLB flush error Xu, Quan
2016-06-13 15:17 ` [PATCH v8 01/11] IOMMU: handle IOMMU mapping and unmapping failures Xu, Quan
2016-06-13 15:17 ` [PATCH v8 02/11] IOMMU/MMU: enhance the call trees of IOMMU unmapping and mapping Xu, Quan
2016-06-13 15:36   ` Jan Beulich
2016-06-13 16:36   ` George Dunlap
2016-06-15  1:54     ` Xu, Quan
2016-06-15  7:44       ` Jan Beulich
2016-06-15  8:15         ` Xu, Quan
2016-06-15  8:22           ` Tian, Kevin
2016-06-15  8:35             ` Xu, Quan
2016-06-15  8:42               ` Jan Beulich
2016-06-15  8:53                 ` Xu, Quan
2016-06-13 15:17 ` [PATCH v8 03/11] IOMMU: propagate IOMMU Device-TLB flush error up to IOMMU unmapping (top level ones) Xu, Quan
2016-06-13 15:17 ` [PATCH v8 04/11] IOMMU: propagate IOMMU Device-TLB flush error up to IOMMU mapping " Xu, Quan
2016-06-15  8:26   ` Xu, Quan
2016-06-16  9:19   ` Julien Grall
2016-06-13 15:17 ` [PATCH v8 05/11] IOMMU/MMU: propagate IOMMU Device-TLB flush error up to iommu_iotlb_flush{, _all} " Xu, Quan
2016-06-13 15:17 ` [PATCH v8 06/11] propagate IOMMU Device-TLB flush error up to EPT update " Xu, Quan
2016-06-13 16:37   ` George Dunlap
2016-06-13 15:17 ` [PATCH v8 07/11] IOMMU: propagate IOMMU Device-TLB flush error up to IOMMU suspending " Xu, Quan
2016-06-13 15:17 ` [PATCH v8 08/11] IOMMU: propagate IOMMU Device-TLB flush error (leaf ones) Xu, Quan
2016-06-16  9:25   ` Julien Grall
2016-06-13 15:17 ` [PATCH v8 09/11] vt-d: fix the IOMMU flush issue Xu, Quan
2016-06-13 15:52   ` Jan Beulich
2016-06-14  8:10     ` Xu, Quan
2016-06-14  8:26       ` Jan Beulich
2016-06-14  9:04         ` Xu, Quan
2016-06-15  1:42           ` Tian, Kevin [this message]
2016-06-13 15:17 ` [PATCH v8 10/11] vt-d: propagate the IOMMU Device-TLB flush error up to ME phantom functions Xu, Quan
2016-06-13 15:17 ` [PATCH v8 11/11] vt-d: add __must_check annotation to IOMMU flush pointers and handlers Xu, Quan

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