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    SubjectRe: [PATCH v5 5/9] iommu/arm-smmu-v3: Refactor write_ctx_desc
    On Tue, Aug 15, 2023 at 7:38 PM Jason Gunthorpe <jgg@nvidia.com> wrote:
    >
    > On Tue, Aug 15, 2023 at 01:20:04PM +0800, Michael Shavit wrote:
    > > On Thu, Aug 10, 2023 at 11:39 PM Jason Gunthorpe <jgg@nvidia.com> wrote:
    > > >
    > > > Actually, I don't think this even works as nothing on the PASID path
    > > > adds to the list that arm_smmu_write_ctx_desc_devices() iterates over ??
    > > >
    > > > Then the remaining two calls:
    > > >
    > > > arm_smmu_share_asid(struct mm_struct *mm, u16 asid)
    > > > arm_smmu_write_ctx_desc_devices(smmu_domain, 0, cd);
    > > >
    > > > This is OK only if the sketchy assumption that the CD
    > > > we extracted for a conflicting ASID is not asigned to a PASID.
    > > >
    > > > static void arm_smmu_mm_release(struct mmu_notifier *mn, struct mm_struct *mm)
    > > > arm_smmu_write_ctx_desc_devices(smmu_domain, mm->pasid, &quiet_cd);
    > > >
    > > > This doesn't work because we didn't add the master to the list
    > > > during __arm_smmu_sva_bind and this path is expressly working
    > > > on the PASID binds, not the RID binds.
    > >
    > > Actually it is working on the RID attached domain (as returned by
    > > iommu_get_domain_for_dev() at sva_bind time) not the SVA domain
    > > here...
    >
    > That can't be right, the purpose of that call and arm_smmu_mm_release is to
    > disable the PASID that is about the UAF the mm's page table.
    >
    > Jason

    For the sake of this message, let's call "primary domain" whatever RID
    domain was attached to a master at the time set_dev_pasid() was called
    on that master. That RID domain is locked in while SVA is enabled and
    cannot be detached.

    The arm-smmu-v3-sva.c implementation creates a mapping between an SVA
    domain and this primary domain (through the sva domain's mm). In
    arm_smmu_mm_release, the primary domain is looked up and
    arm_smmu_write_ctx_desc() is called on all masters that this domain is
    attached to.

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