Messages in this thread | | | Subject | Re: [PATCH v5 4/7] iommu: Factor iommu_iotlb_gather_is_disjoint() out | From | Robin Murphy <> | Date | Tue, 13 Jul 2021 19:25:18 +0100 |
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On 2021-07-13 10:41, Nadav Amit wrote: > From: Nadav Amit <namit@vmware.com> > > Refactor iommu_iotlb_gather_add_page() and factor out the logic that > detects whether IOTLB gather range and a new range are disjoint. To be > used by the next patch that implements different gathering logic for > AMD. > > Note that updating gather->pgsize unconditionally does not affect > correctness as the function had (and has) an invariant, in which > gather->pgsize always represents the flushing granularity of its range. > Arguably, “size" should never be zero, but lets assume for the matter of > discussion that it might. > > If "size" equals to "gather->pgsize", then the assignment in question > has no impact. > > Otherwise, if "size" is non-zero, then iommu_iotlb_sync() would > initialize the size and range (see iommu_iotlb_gather_init()), and the > invariant is kept. > > Otherwise, "size" is zero, and "gather" already holds a range, so > gather->pgsize is non-zero and (gather->pgsize && gather->pgsize != > size) is true. Therefore, again, iommu_iotlb_sync() would be called and > initialize the size.
With the caveat of one comment on the next patch...
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
> Cc: Joerg Roedel <joro@8bytes.org> > Cc: Jiajun Cao <caojiajun@vmware.com> > Cc: Robin Murphy <robin.murphy@arm.com> > Cc: Lu Baolu <baolu.lu@linux.intel.com> > Cc: iommu@lists.linux-foundation.org > Cc: linux-kernel@vger.kernel.org> > Acked-by: Will Deacon <will@kernel.org> > Signed-off-by: Nadav Amit <namit@vmware.com> > --- > include/linux/iommu.h | 34 ++++++++++++++++++++++++++-------- > 1 file changed, 26 insertions(+), 8 deletions(-) > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h > index e554871db46f..979a5ceeea55 100644 > --- a/include/linux/iommu.h > +++ b/include/linux/iommu.h > @@ -497,6 +497,28 @@ static inline void iommu_iotlb_sync(struct iommu_domain *domain, > iommu_iotlb_gather_init(iotlb_gather); > } > > +/** > + * iommu_iotlb_gather_is_disjoint - Checks whether a new range is disjoint > + * > + * @gather: TLB gather data > + * @iova: start of page to invalidate > + * @size: size of page to invalidate > + * > + * Helper for IOMMU drivers to check whether a new range and the gathered range > + * are disjoint. For many IOMMUs, flushing the IOMMU in this case is better > + * than merging the two, which might lead to unnecessary invalidations. > + */ > +static inline > +bool iommu_iotlb_gather_is_disjoint(struct iommu_iotlb_gather *gather, > + unsigned long iova, size_t size) > +{ > + unsigned long start = iova, end = start + size - 1; > + > + return gather->end != 0 && > + (end + 1 < gather->start || start > gather->end + 1); > +} > + > + > /** > * iommu_iotlb_gather_add_range - Gather for address-based TLB invalidation > * @gather: TLB gather data > @@ -533,20 +555,16 @@ static inline void iommu_iotlb_gather_add_page(struct iommu_domain *domain, > struct iommu_iotlb_gather *gather, > unsigned long iova, size_t size) > { > - unsigned long start = iova, end = start + size - 1; > - > /* > * If the new page is disjoint from the current range or is mapped at > * a different granularity, then sync the TLB so that the gather > * structure can be rewritten. > */ > - if (gather->pgsize != size || > - end + 1 < gather->start || start > gather->end + 1) { > - if (gather->pgsize) > - iommu_iotlb_sync(domain, gather); > - gather->pgsize = size; > - } > + if ((gather->pgsize && gather->pgsize != size) || > + iommu_iotlb_gather_is_disjoint(gather, iova, size)) > + iommu_iotlb_sync(domain, gather); > > + gather->pgsize = size; > iommu_iotlb_gather_add_range(gather, iova, size); > } > >
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