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e57e58bd39
Holding mm_users works OK for graphics, which was the first user of SVM with VT-d. However, it works less well for other devices, where we actually do a mmap() from the file descriptor to which the SVM PASID state is tied. In this case on process exit we end up with a recursive reference count: - The MM remains alive until the file is closed and the driver's release() call ends up unbinding the PASID. - The VMA corresponding to the mmap() remains intact until the MM is destroyed. - Thus the file isn't closed, even when exit_files() runs, because the VMA is still holding a reference to it. And the MM remains alive… To address this issue, we *stop* holding mm_users while the PASID is bound. We already hold mm_count by virtue of the MMU notifier, and that can be made to be sufficient. It means that for a period during process exit, the fun part of mmput() has happened and exit_mmap() has been called so the MM is basically defunct. But the PGD still exists and the PASID is still bound to it. During this period, we have to be very careful — exit_mmap() doesn't use mm->mmap_sem because it doesn't expect anyone else to be touching the MM (quite reasonably, since mm_users is zero). So we also need to fix the fault handler to just report failure if mm_users is already zero, and to temporarily bump mm_users while handling any faults. Additionally, exit_mmap() calls mmu_notifier_release() *before* it tears down the page tables, which is too early for us to flush the IOTLB for this PASID. And __mmu_notifier_release() removes every notifier from the list, so when exit_mmap() finally *does* tear down the mappings and clear the page tables, we don't get notified. So we work around this by clearing the PASID table entry in our MMU notifier release() callback. That way, the hardware *can't* get any pages back from the page tables before they get cleared. Hardware designers have confirmed that the resulting 'PASID not present' faults should be handled just as gracefully as 'page not present' faults, the important criterion being that they don't perturb the operation for any *other* PASID in the system. Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Cc: stable@vger.kernel.org |
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| .. | ||
| amd_iommu_init.c | ||
| amd_iommu_proto.h | ||
| amd_iommu_types.h | ||
| amd_iommu_v2.c | ||
| amd_iommu.c | ||
| arm-smmu-v3.c | ||
| arm-smmu.c | ||
| dma-iommu.c | ||
| dmar.c | ||
| exynos-iommu.c | ||
| fsl_pamu_domain.c | ||
| fsl_pamu_domain.h | ||
| fsl_pamu.c | ||
| fsl_pamu.h | ||
| intel_irq_remapping.c | ||
| intel-iommu.c | ||
| intel-svm.c | ||
| io-pgtable-arm.c | ||
| io-pgtable.c | ||
| io-pgtable.h | ||
| iommu-sysfs.c | ||
| iommu-traces.c | ||
| iommu.c | ||
| iova.c | ||
| ipmmu-vmsa.c | ||
| irq_remapping.c | ||
| irq_remapping.h | ||
| Kconfig | ||
| Makefile | ||
| msm_iommu_dev.c | ||
| msm_iommu_hw-8xxx.h | ||
| msm_iommu.c | ||
| msm_iommu.h | ||
| of_iommu.c | ||
| omap-iommu-debug.c | ||
| omap-iommu.c | ||
| omap-iommu.h | ||
| omap-iopgtable.h | ||
| rockchip-iommu.c | ||
| s390-iommu.c | ||
| shmobile-iommu.c | ||
| shmobile-ipmmu.c | ||
| shmobile-ipmmu.h | ||
| tegra-gart.c | ||
| tegra-smmu.c | ||