From: Omar Elghoul <[email protected]> When s390_pci_update_iotlb() does a mapping update for an IOVA that has an already-existing TLB entry with different permissions or translated address, it unmaps then remaps it. However, at the end of the map path, it unconditionally decrements the available DMA slot counter without a corresponding increment in the intermediate unmap branch.
This causes the DMA slot count to be decremented on every remapping of an active IOVA, leading to a permanent DMA slot leak. This remapping without a prior invalidation and sync is not seen today in well-behaved guests but is allowed by the architecture. Fix it by only decrementing available DMA slots when inserting a brand new mapping. Cc: [email protected] Fixes: 37fa32de70 ("s390x/pci: Honor DMA limits set by vfio") Signed-off-by: Omar Elghoul <[email protected]> Reviewed-by: Farhan Ali <[email protected]> Reviewed-by: Matthew Rosato <[email protected]> Link: https://lore.kernel.org/qemu-devel/[email protected] Signed-off-by: Eric Farman <[email protected]> --- hw/s390x/s390-pci-inst.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/hw/s390x/s390-pci-inst.c b/hw/s390x/s390-pci-inst.c index b7de23c7d2..652e1712ec 100644 --- a/hw/s390x/s390-pci-inst.c +++ b/hw/s390x/s390-pci-inst.c @@ -655,6 +655,7 @@ static uint32_t s390_pci_update_iotlb(S390PCIIOMMU *iommu, goto out; } else { if (cache) { + /* valid->valid transitions reuse the DMA slot */ if (cache->perm == entry->perm && cache->translated_addr == entry->translated_addr) { goto out; @@ -665,6 +666,9 @@ static uint32_t s390_pci_update_iotlb(S390PCIIOMMU *iommu, memory_region_notify_iommu(&iommu->iommu_mr, 0, event); event.type = IOMMU_NOTIFIER_MAP; event.entry.perm = entry->perm; + } else { + /* invalid->valid transitions consume a new DMA slot */ + dec_dma_avail(iommu); } cache = g_new(S390IOTLBEntry, 1); @@ -673,7 +677,6 @@ static uint32_t s390_pci_update_iotlb(S390PCIIOMMU *iommu, cache->len = TARGET_PAGE_SIZE; cache->perm = entry->perm; g_hash_table_replace(iommu->iotlb, &cache->iova, cache); - dec_dma_avail(iommu); } /* -- 2.55.0
