From 9b64b3cc833eaec290e65bc0958aeb51c6892152 Mon Sep 17 00:00:00 2001 From: Omar Elghoul Date: Thu, 17 Sep 2026 10:04:31 -0400 Subject: [PATCH] s390x/pci: fix DMA slot leak on I/O TLB entry replacement 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: qemu-stable@nongnu.org Fixes: 37fa32de70 ("s390x/pci: Honor DMA limits set by vfio") Signed-off-by: Omar Elghoul Reviewed-by: Farhan Ali Reviewed-by: Matthew Rosato Link: https://lore.kernel.org/qemu-devel/20260917140431.45343-1-oelghoul@linux.ibm.com Signed-off-by: Eric Farman --- 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); } /*