> Let's query the maximum number of DMA mappings by querying the available
> mappings when creating the container.
>
> In addition, count the number of DMA mappings and warn when we would
> exceed it. This is a preparation for RamDiscardMgr which might
> create quite some DMA mappings over time, and we at least want to warn
> early that the QEMU setup might be problematic. Use "reserved"
> terminology, so we can use this to reserve mappings before they are
> actually created.
>
> Note: don't reserve vIOMMU DMA mappings - using the vIOMMU region size
> divided by the mapping page size might be a bad indication of what will
> happen in practice - we might end up warning all the time.
>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: "Michael S. Tsirkin" <m...@redhat.com>
> Cc: Alex Williamson <alex.william...@redhat.com>
> Cc: Dr. David Alan Gilbert <dgilb...@redhat.com>
> Cc: Igor Mammedov <imamm...@redhat.com>
> Cc: Pankaj Gupta <pankaj.gupta.li...@gmail.com>
> Cc: Peter Xu <pet...@redhat.com>
> Cc: Auger Eric <eric.au...@redhat.com>
> Cc: Wei Yang <richard.weiy...@linux.alibaba.com>
> Cc: teawater <teawat...@linux.alibaba.com>
> Cc: Marek Kedzierski <mkedz...@redhat.com>
> Signed-off-by: David Hildenbrand <da...@redhat.com>
> ---
> hw/vfio/common.c | 34 ++++++++++++++++++++++++++++++++++
> include/hw/vfio/vfio-common.h | 2 ++
> 2 files changed, 36 insertions(+)
>
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 6ff1daa763..5ad88d476f 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -288,6 +288,26 @@ const MemoryRegionOps vfio_region_ops = {
> },
> };
>
> +static void vfio_container_dma_reserve(VFIOContainer *container,
> + unsigned long dma_mappings)
> +{
> + bool warned = container->dma_reserved > container->dma_max;
> +
> + container->dma_reserved += dma_mappings;
> + if (!warned && container->dma_max &&
> + container->dma_reserved > container->dma_max) {
> + warn_report("%s: possibly running out of DMA mappings. "
> + " Maximum number of DMA mappings: %d", __func__,
> + container->dma_max);
> + }
> +}
> +
> +static void vfio_container_dma_unreserve(VFIOContainer *container,
> + unsigned long dma_mappings)
> +{
> + container->dma_reserved -= dma_mappings;
> +}
> +
> /*
> * Device state interfaces
> */
> @@ -835,6 +855,9 @@ static void vfio_listener_region_add(MemoryListener
> *listener,
> }
> }
>
> + /* We'll need one DMA mapping. */
> + vfio_container_dma_reserve(container, 1);
> +
> ret = vfio_dma_map(container, iova, int128_get64(llsize),
> vaddr, section->readonly);
> if (ret) {
> @@ -879,6 +902,7 @@ static void vfio_listener_region_del(MemoryListener
> *listener,
> MemoryRegionSection *section)
> {
> VFIOContainer *container = container_of(listener, VFIOContainer,
> listener);
> + bool unreserve_on_unmap = true;
> hwaddr iova, end;
> Int128 llend, llsize;
> int ret;
> @@ -919,6 +943,7 @@ static void vfio_listener_region_del(MemoryListener
> *listener,
> * based IOMMU where a big unmap flattens a large range of IO-PTEs.
> * That may not be true for all IOMMU types.
> */
> + unreserve_on_unmap = false;
> }
>
> iova = TARGET_PAGE_ALIGN(section->offset_within_address_space);
> @@ -970,6 +995,11 @@ static void vfio_listener_region_del(MemoryListener
> *listener,
> "0x%"HWADDR_PRIx") = %d (%m)",
> container, iova, int128_get64(llsize), ret);
> }
> +
> + /* We previously reserved one DMA mapping. */
> + if (unreserve_on_unmap) {
> + vfio_container_dma_unreserve(container, 1);
> + }
> }
>
> memory_region_unref(section->mr);
> @@ -1735,6 +1765,7 @@ static int vfio_connect_container(VFIOGroup *group,
> AddressSpace *as,
> container->fd = fd;
> container->error = NULL;
> container->dirty_pages_supported = false;
> + container->dma_max = 0;
> QLIST_INIT(&container->giommu_list);
> QLIST_INIT(&container->hostwin_list);
>
> @@ -1765,7 +1796,10 @@ static int vfio_connect_container(VFIOGroup *group,
> AddressSpace *as,
> vfio_host_win_add(container, 0, (hwaddr)-1, info->iova_pgsizes);
> container->pgsizes = info->iova_pgsizes;
>
> + /* The default in the kernel ("dma_entry_limit") is 65535. */
> + container->dma_max = 65535;
> if (!ret) {
> + vfio_get_info_dma_avail(info, &container->dma_max);
> vfio_get_iommu_info_migration(container, info);
> }
> g_free(info);
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index 6141162d7a..fed0e85f66 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -88,6 +88,8 @@ typedef struct VFIOContainer {
> uint64_t dirty_pgsizes;
> uint64_t max_dirty_bitmap_size;
> unsigned long pgsizes;
> + unsigned int dma_max;
> + unsigned long dma_reserved;
> QLIST_HEAD(, VFIOGuestIOMMU) giommu_list;
> QLIST_HEAD(, VFIOHostDMAWindow) hostwin_list;
> QLIST_HEAD(, VFIOGroup) group_list;
Reviewed-by: Pankaj Gupta <pankaj.gu...@cloud.ionos.com>
