When quickly unmapping and mapping memory regions (as may happen in address_space_update_topology), if running with a non-unlimited RLIMIT_MEMLOCK, the kernel may return ENOMEM for a map request because the previous unmap has been processed, but accounted yet.
Probably this should be fixed in the kernel ensuring a deterministic behavior for VFIO map and unmap operations. Until then, this works around the issue, waiting 10ms and trying again. Signed-off-by: Sergio Lopez <s...@redhat.com> --- hw/vfio/common.c | 31 +++++++++++++++++++++++-------- 1 file changed, 23 insertions(+), 8 deletions(-) diff --git a/hw/vfio/common.c b/hw/vfio/common.c index f3ba9b9..db41fa5 100644 --- a/hw/vfio/common.c +++ b/hw/vfio/common.c @@ -228,17 +228,32 @@ static int vfio_dma_map(VFIOContainer *container, hwaddr iova, map.flags |= VFIO_DMA_MAP_FLAG_WRITE; } - /* - * Try the mapping, if it fails with EBUSY, unmap the region and try - * again. This shouldn't be necessary, but we sometimes see it in - * the VGA ROM space. - */ - if (ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map) == 0 || - (errno == EBUSY && vfio_dma_unmap(container, iova, size) == 0 && - ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map) == 0)) { + if (ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map) == 0) { return 0; } + if (errno == ENOMEM) { + /* + * When quickly unmapping and mapping ranges, the kernel may + * return ENOMEM for a map request because the previous unmap + * has not been accounted yet. Wait a bit and try again. + */ + usleep(10 * 1000); + if (ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map) == 0) { + return 0; + } + } else if (errno == EBUSY) { + /* + * If mapping fails with EBUSY, unmap the region and try again. + * This shouldn't be necessary, but we sometimes see it in the + * VGA ROM space. + */ + if (vfio_dma_unmap(container, iova, size) == 0 && + ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map) == 0) { + return 0; + } + } + error_report("VFIO_MAP_DMA: %d", -errno); return -errno; } -- 2.9.3