86 lines
2.7 KiB
Diff
86 lines
2.7 KiB
Diff
From 32803dc7c2ffc29db15a46034d818f6e6c5775ef Mon Sep 17 00:00:00 2001
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From: Ajay Garg <ajaygargnsit@gmail.com>
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Date: Tue, 12 Oct 2021 19:26:53 +0530
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Subject: [PATCH] iommu: intel: do deep dma-unmapping, to avoid
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kernel-flooding.
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Origins at :
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https://lists.linuxfoundation.org/pipermail/iommu/2021-October/thread.html
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=== Changes from v1 => v2 ===
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a)
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Improved patch-description.
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b)
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A more root-level fix, as suggested by
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1.
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Alex Williamson <alex.williamson@redhat.com>
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2.
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Lu Baolu <baolu.lu@linux.intel.com>
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=== Issue ===
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Kernel-flooding is seen, when an x86_64 L1 guest (Ubuntu-21) is booted in qemu/kvm
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on a x86_64 host (Ubuntu-21), with a host-pci-device attached.
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Following kind of logs, along with the stacktraces, cause the flood :
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......
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DMAR: ERROR: DMA PTE for vPFN 0x428ec already set (to 3f6ec003 not 3f6ec003)
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DMAR: ERROR: DMA PTE for vPFN 0x428ed already set (to 3f6ed003 not 3f6ed003)
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DMAR: ERROR: DMA PTE for vPFN 0x428ee already set (to 3f6ee003 not 3f6ee003)
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DMAR: ERROR: DMA PTE for vPFN 0x428ef already set (to 3f6ef003 not 3f6ef003)
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DMAR: ERROR: DMA PTE for vPFN 0x428f0 already set (to 3f6f0003 not 3f6f0003)
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......
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=== Current Behaviour, leading to the issue ===
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Currently, when we do a dma-unmapping, we unmap/unlink the mappings, but
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the pte-entries are not cleared.
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Thus, following sequencing would flood the kernel-logs :
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i)
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A dma-unmapping makes the real/leaf-level pte-slot invalid, but the
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pte-content itself is not cleared.
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ii)
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Now, during some later dma-mapping procedure, as the pte-slot is about
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to hold a new pte-value, the intel-iommu checks if a prior
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pte-entry exists in the pte-slot. If it exists, it logs a kernel-error,
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along with a corresponding stacktrace.
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iii)
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Step ii) runs in abundance, and the kernel-logs run insane.
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=== Fix ===
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We ensure that as part of a dma-unmapping, each (unmapped) pte-slot
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is also cleared of its value/content (at the leaf-level, where the
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real mapping from a iova => pfn mapping is stored).
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This completes a "deep" dma-unmapping.
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Signed-off-by: Ajay Garg <ajaygargnsit@gmail.com>
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Link: https://lore.kernel.org/linux-iommu/20211012135653.3852-1-ajaygargnsit@gmail.com/
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---
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drivers/iommu/intel/iommu.c | 2 ++
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1 file changed, 2 insertions(+)
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diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
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index 78f8c8e6803e9..d8da48a91ba3b 100644
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--- a/drivers/iommu/intel/iommu.c
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+++ b/drivers/iommu/intel/iommu.c
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@@ -5092,6 +5092,8 @@ static size_t intel_iommu_unmap(struct iommu_domain *domain,
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gather->freelist = domain_unmap(dmar_domain, start_pfn,
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last_pfn, gather->freelist);
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+ dma_pte_clear_range(dmar_domain, start_pfn, last_pfn);
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+
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if (dmar_domain->max_addr == iova + size)
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dmar_domain->max_addr = iova;
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