diff options
Diffstat (limited to 'libre/linux-libre-pae/0003-iommu-intel-do-deep-dma-unmapping-to-avoid-kernel-fl.patch')
| -rw-r--r-- | libre/linux-libre-pae/0003-iommu-intel-do-deep-dma-unmapping-to-avoid-kernel-fl.patch | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/libre/linux-libre-pae/0003-iommu-intel-do-deep-dma-unmapping-to-avoid-kernel-fl.patch b/libre/linux-libre-pae/0003-iommu-intel-do-deep-dma-unmapping-to-avoid-kernel-fl.patch new file mode 100644 index 000000000..567806cbd --- /dev/null +++ b/libre/linux-libre-pae/0003-iommu-intel-do-deep-dma-unmapping-to-avoid-kernel-fl.patch @@ -0,0 +1,88 @@ +From 8ae0cfc0b59cd1462ca6cd819878933d357d01a7 Mon Sep 17 00:00:00 2001 +From: Ajay Garg <ajaygargnsit@gmail.com> +Date: Tue, 12 Oct 2021 19:26:53 +0530 +Subject: [PATCH 3/6] iommu: intel: do deep dma-unmapping, to avoid + kernel-flooding. + +Origins at : +https://lists.linuxfoundation.org/pipermail/iommu/2021-October/thread.html + +=== Changes from v1 => v2 === + +a) +Improved patch-description. + +b) +A more root-level fix, as suggested by + + 1. + Alex Williamson <alex.williamson@redhat.com> + + 2. + Lu Baolu <baolu.lu@linux.intel.com> + +=== Issue === + +Kernel-flooding is seen, when an x86_64 L1 guest (Ubuntu-21) is booted in qemu/kvm +on a x86_64 host (Ubuntu-21), with a host-pci-device attached. + +Following kind of logs, along with the stacktraces, cause the flood : + +...... + DMAR: ERROR: DMA PTE for vPFN 0x428ec already set (to 3f6ec003 not 3f6ec003) + DMAR: ERROR: DMA PTE for vPFN 0x428ed already set (to 3f6ed003 not 3f6ed003) + DMAR: ERROR: DMA PTE for vPFN 0x428ee already set (to 3f6ee003 not 3f6ee003) + DMAR: ERROR: DMA PTE for vPFN 0x428ef already set (to 3f6ef003 not 3f6ef003) + DMAR: ERROR: DMA PTE for vPFN 0x428f0 already set (to 3f6f0003 not 3f6f0003) +...... + +=== Current Behaviour, leading to the issue === + +Currently, when we do a dma-unmapping, we unmap/unlink the mappings, but +the pte-entries are not cleared. + +Thus, following sequencing would flood the kernel-logs : + +i) +A dma-unmapping makes the real/leaf-level pte-slot invalid, but the +pte-content itself is not cleared. + +ii) +Now, during some later dma-mapping procedure, as the pte-slot is about +to hold a new pte-value, the intel-iommu checks if a prior +pte-entry exists in the pte-slot. If it exists, it logs a kernel-error, +along with a corresponding stacktrace. + +iii) +Step ii) runs in abundance, and the kernel-logs run insane. + +=== Fix === + +We ensure that as part of a dma-unmapping, each (unmapped) pte-slot +is also cleared of its value/content (at the leaf-level, where the +real mapping from a iova => pfn mapping is stored). + +This completes a "deep" dma-unmapping. + +Signed-off-by: Ajay Garg <ajaygargnsit@gmail.com> +Link: https://lore.kernel.org/linux-iommu/20211012135653.3852-1-ajaygargnsit@gmail.com/ +--- + drivers/iommu/intel/iommu.c | 2 ++ + 1 file changed, 2 insertions(+) + +diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c +index 78f8c8e6803e..d8da48a91ba3 100644 +--- a/drivers/iommu/intel/iommu.c ++++ b/drivers/iommu/intel/iommu.c +@@ -5092,6 +5092,8 @@ static size_t intel_iommu_unmap(struct iommu_domain *domain, + gather->freelist = domain_unmap(dmar_domain, start_pfn, + last_pfn, gather->freelist); + ++ dma_pte_clear_range(dmar_domain, start_pfn, last_pfn); ++ + if (dmar_domain->max_addr == iova + size) + dmar_domain->max_addr = iova; + +-- +2.34.1 + |