From: "Durrant, Paul" <pdurrant@amazon.co.uk>
To: "Tian, Kevin" <kevin.tian@intel.com>, Paul Durrant <paul@xen.org>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Jan Beulich <jbeulich@suse.com>
Subject: RE: [PATCH v4 06/14] iommu: flush I/O TLB if iommu_map() or iommu_unmap() fail
Date: Fri, 14 Aug 2020 07:19:14 +0000 [thread overview]
Message-ID: <90778935e1334f838e3d41d4171ac8ff@EX13D32EUC003.ant.amazon.com> (raw)
In-Reply-To: <MWHPR11MB16450DC48C30E2A4770B91BC8C400@MWHPR11MB1645.namprd11.prod.outlook.com>
> -----Original Message-----
> From: Tian, Kevin <kevin.tian@intel.com>
> Sent: 14 August 2020 07:53
> To: Paul Durrant <paul@xen.org>; xen-devel@lists.xenproject.org
> Cc: Durrant, Paul <pdurrant@amazon.co.uk>; Jan Beulich <jbeulich@suse.com>
> Subject: RE: [EXTERNAL] [PATCH v4 06/14] iommu: flush I/O TLB if iommu_map() or iommu_unmap() fail
>
> CAUTION: This email originated from outside of the organization. Do not click links or open
> attachments unless you can confirm the sender and know the content is safe.
>
>
>
> > From: Paul Durrant
> > Sent: Tuesday, August 4, 2020 9:42 PM
> >
> > From: Paul Durrant <pdurrant@amazon.com>
> >
> > This patch adds a full I/O TLB flush to the error paths of iommu_map() and
> > iommu_unmap().
> >
> > Without this change callers need constructs such as:
> >
> > rc = iommu_map/unmap(...)
> > err = iommu_flush(...)
> > if ( !rc )
> > rc = err;
> >
> > With this change, it can be simplified to:
> >
> > rc = iommu_map/unmap(...)
> > if ( !rc )
> > rc = iommu_flush(...)
> >
> > because, if the map or unmap fails the flush will be unnecessary. This saves
>
> this statement is different from change in iommu_map...
>
> > a stack variable and generally makes the call sites tidier.
> >
> > Signed-off-by: Paul Durrant <pdurrant@amazon.com>
> > ---
> > Cc: Jan Beulich <jbeulich@suse.com>
> >
> > v2:
> > - New in v2
> > ---
> > xen/drivers/passthrough/iommu.c | 28 ++++++++++++----------------
> > 1 file changed, 12 insertions(+), 16 deletions(-)
> >
> > diff --git a/xen/drivers/passthrough/iommu.c
> > b/xen/drivers/passthrough/iommu.c
> > index 660dc5deb2..e2c0193a09 100644
> > --- a/xen/drivers/passthrough/iommu.c
> > +++ b/xen/drivers/passthrough/iommu.c
> > @@ -274,6 +274,10 @@ int iommu_map(struct domain *d, dfn_t dfn, mfn_t
> > mfn,
> > break;
> > }
> >
> > + /* Something went wrong so flush everything and clear flush flags */
> > + if ( unlikely(rc) && iommu_iotlb_flush_all(d, *flush_flags) )
> > + flush_flags = 0;
> > +
>
> ... earlier you said flush is unnecessary if map fails. But here actually you
> still need to flush everything so it's just sort of moving error-path flush
> within the map function?
Yes, that's actually what's happening. The language in the comment is ambiguous I guess. I'll modify it to say
"because, if the map or unmap fails an explicit flush will be unnecessary."
Hopefully that is clearer.
Paul
>
> Thanks
> Kevin
>
> > return rc;
> > }
> >
> > @@ -283,14 +287,8 @@ int iommu_legacy_map(struct domain *d, dfn_t dfn,
> > mfn_t mfn,
> > unsigned int flush_flags = 0;
> > int rc = iommu_map(d, dfn, mfn, page_order, flags, &flush_flags);
> >
> > - if ( !this_cpu(iommu_dont_flush_iotlb) )
> > - {
> > - int err = iommu_iotlb_flush(d, dfn, (1u << page_order),
> > - flush_flags);
> > -
> > - if ( !rc )
> > - rc = err;
> > - }
> > + if ( !this_cpu(iommu_dont_flush_iotlb) && !rc )
> > + rc = iommu_iotlb_flush(d, dfn, (1u << page_order), flush_flags);
> >
> > return rc;
> > }
> > @@ -330,6 +328,10 @@ int iommu_unmap(struct domain *d, dfn_t dfn,
> > unsigned int page_order,
> > }
> > }
> >
> > + /* Something went wrong so flush everything and clear flush flags */
> > + if ( unlikely(rc) && iommu_iotlb_flush_all(d, *flush_flags) )
> > + flush_flags = 0;
> > +
> > return rc;
> > }
> >
> > @@ -338,14 +340,8 @@ int iommu_legacy_unmap(struct domain *d, dfn_t
> > dfn, unsigned int page_order)
> > unsigned int flush_flags = 0;
> > int rc = iommu_unmap(d, dfn, page_order, &flush_flags);
> >
> > - if ( !this_cpu(iommu_dont_flush_iotlb) )
> > - {
> > - int err = iommu_iotlb_flush(d, dfn, (1u << page_order),
> > - flush_flags);
> > -
> > - if ( !rc )
> > - rc = err;
> > - }
> > + if ( !this_cpu(iommu_dont_flush_iotlb) && ! rc )
> > + rc = iommu_iotlb_flush(d, dfn, (1u << page_order), flush_flags);
> >
> > return rc;
> > }
> > --
> > 2.20.1
> >
next prev parent reply other threads:[~2020-08-14 7:19 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-04 13:41 [PATCH v4 00/14] IOMMU cleanup Paul Durrant
2020-08-04 13:41 ` [PATCH v4 01/14] x86/iommu: re-arrange arch_iommu to separate common fields Paul Durrant
2020-08-14 6:14 ` Tian, Kevin
2020-08-04 13:41 ` [PATCH v4 02/14] x86/iommu: add common page-table allocator Paul Durrant
2020-08-05 15:39 ` Jan Beulich
2020-08-04 13:41 ` [PATCH v4 03/14] x86/iommu: convert VT-d code to use new page table allocator Paul Durrant
2020-08-14 6:41 ` Tian, Kevin
2020-08-14 7:16 ` Durrant, Paul
2020-08-04 13:41 ` [PATCH v4 04/14] x86/iommu: convert AMD IOMMU " Paul Durrant
2020-08-04 13:42 ` [PATCH v4 05/14] iommu: remove unused iommu_ops method and tasklet Paul Durrant
2020-08-04 13:42 ` [PATCH v4 06/14] iommu: flush I/O TLB if iommu_map() or iommu_unmap() fail Paul Durrant
2020-08-05 16:06 ` Jan Beulich
2020-08-05 16:18 ` Paul Durrant
2020-08-06 11:41 ` Jan Beulich
2020-08-14 6:53 ` Tian, Kevin
2020-08-14 7:19 ` Durrant, Paul [this message]
2020-08-04 13:42 ` [PATCH v4 07/14] iommu: make map, unmap and flush all take both an order and a count Paul Durrant
2020-08-06 9:57 ` Jan Beulich
2020-08-11 11:00 ` Durrant, Paul
2020-08-14 6:57 ` Tian, Kevin
2020-08-04 13:42 ` [PATCH v4 08/14] remove remaining uses of iommu_legacy_map/unmap Paul Durrant
2020-08-06 10:28 ` Jan Beulich
2020-08-12 9:36 ` [EXTERNAL] " Paul Durrant
2020-08-04 13:42 ` [PATCH v4 09/14] common/grant_table: batch flush I/O TLB Paul Durrant
2020-08-06 11:49 ` Jan Beulich
2020-08-04 13:42 ` [PATCH v4 10/14] iommu: remove the share_p2m operation Paul Durrant
2020-08-06 12:18 ` Jan Beulich
2020-08-14 7:04 ` Tian, Kevin
2020-08-04 13:42 ` [PATCH v4 11/14] iommu: stop calling IOMMU page tables 'p2m tables' Paul Durrant
2020-08-06 12:23 ` Jan Beulich
2020-08-14 7:12 ` Tian, Kevin
2020-08-04 13:42 ` [PATCH v4 12/14] vtd: use a bit field for root_entry Paul Durrant
2020-08-06 12:34 ` Jan Beulich
2020-08-12 13:13 ` Durrant, Paul
2020-08-18 8:27 ` Jan Beulich
2020-08-14 7:17 ` Tian, Kevin
2020-08-04 13:42 ` [PATCH v4 13/14] vtd: use a bit field for context_entry Paul Durrant
2020-08-06 12:46 ` Jan Beulich
2020-08-12 13:47 ` Paul Durrant
2020-08-14 7:19 ` Tian, Kevin
2020-08-04 13:42 ` [PATCH v4 14/14] vtd: use a bit field for dma_pte Paul Durrant
2020-08-06 12:53 ` Jan Beulich
2020-08-12 13:49 ` Paul Durrant
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