Messages in this thread | | | From | Nadav Amit <> | Subject | Re: [PATCH v3 6/6] iommu/amd: Sync once for scatter-gather operations | Date | Tue, 15 Jun 2021 18:51:08 +0000 |
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> On Jun 15, 2021, at 4:25 AM, Robin Murphy <robin.murphy@arm.com> wrote: > > On 2021-06-07 19:25, Nadav Amit wrote: >> From: Nadav Amit <namit@vmware.com> >> On virtual machines, software must flush the IOTLB after each page table >> entry update. >> The iommu_map_sg() code iterates through the given scatter-gather list >> and invokes iommu_map() for each element in the scatter-gather list, >> which calls into the vendor IOMMU driver through iommu_ops callback. As >> the result, a single sg mapping may lead to multiple IOTLB flushes. >> Fix this by adding amd_iotlb_sync_map() callback and flushing at this >> point after all sg mappings we set. >> This commit is followed and inspired by commit 933fcd01e97e2 >> ("iommu/vt-d: Add iotlb_sync_map callback"). >> Cc: Joerg Roedel <joro@8bytes.org> >> Cc: Will Deacon <will@kernel.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 >> Signed-off-by: Nadav Amit <namit@vmware.com> >> --- >> drivers/iommu/amd/iommu.c | 15 ++++++++++++--- >> 1 file changed, 12 insertions(+), 3 deletions(-) >> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c >> index 128f2e889ced..dd23566f1db8 100644 >> --- a/drivers/iommu/amd/iommu.c >> +++ b/drivers/iommu/amd/iommu.c >> @@ -2027,6 +2027,16 @@ static int amd_iommu_attach_device(struct iommu_domain *dom, >> return ret; >> } >> +static void amd_iommu_iotlb_sync_map(struct iommu_domain *dom, >> + unsigned long iova, size_t size) >> +{ >> + struct protection_domain *domain = to_pdomain(dom); >> + struct io_pgtable_ops *ops = &domain->iop.iop.ops; >> + >> + if (ops->map) > > Not too critical since you're only moving existing code around, but is ops->map ever not set? Either way the check ends up looking rather out-of-place here :/ > > It's not very clear what the original intent was - I do wonder whether it's supposed to be related to PAGE_MODE_NONE, but given that amd_iommu_map() has an explicit check and errors out early in that case, we'd never get here anyway. Possibly something to come back and clean up later?
[ +Suravee ]
According to what I see in the git log, the checks for ops->map (as well as ops->unmap) were relatively recently introduced by Suravee [1] in preparation to AMD IOMMU v2 page tables [2]. Since I do not know what he plans, I prefer not to touch this code.
[1] https://lore.kernel.org/linux-iommu/20200923101442.73157-13-suravee.suthikulpanit@amd.com/ [2] https://lore.kernel.org/linux-iommu/20200923101442.73157-1-suravee.suthikulpanit@amd.com/
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