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-rw-r--r--libre/linux-libre-pae/0003-iommu-intel-do-deep-dma-unmapping-to-avoid-kernel-fl.patch88
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
+