567d7d3e6b
A kernel bug was introduced in v4.15 via commit 71a7d3d78e3c which adds a test for address space wrap-around in the vfio DMA unmap path. Unfortunately due to overflow, the kernel detects an unmap of the last page in the 64-bit address space as a wrap-around. In QEMU, a Q35 guest with VT-d emulation and guest IOMMU enabled will attempt to make such an unmap request during VM system reset, triggering an error: qemu-kvm: VFIO_UNMAP_DMA: -22 qemu-kvm: vfio_dma_unmap(0x561f059948f0, 0xfef00000, 0xffffffff01100000) = -22 (Invalid argument) Here the IOVA start address (0xfef00000) and the size parameter (0xffffffff01100000) add to exactly 2^64, triggering the bug. A kernel fix is queued for the Linux v5.0 release to address this. This patch implements a workaround to retry the unmap, excluding the final page of the range when we detect an unmap failing which matches the requirements for this issue. This is expected to be a safe and complete workaround as the VT-d address space does not extend to the full 64-bit space and therefore the last page should never be mapped. This workaround can be removed once all kernels with this bug are sufficiently deprecated. Link: https://bugzilla.redhat.com/show_bug.cgi?id=1662291 Reported-by: Pei Zhang <pezhang@redhat.com> Debugged-by: Peter Xu <peterx@redhat.com> Reviewed-by: Peter Xu <peterx@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Signed-off-by: Alex Williamson <alex.williamson@redhat.com> |
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| .. | ||
| amd-xgbe.c | ||
| ap.c | ||
| calxeda-xgmac.c | ||
| ccw.c | ||
| common.c | ||
| display.c | ||
| Makefile.objs | ||
| pci-quirks.c | ||
| pci.c | ||
| pci.h | ||
| platform.c | ||
| spapr.c | ||
| trace-events | ||