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vfio: Sanity check maximum number of DMA mappings with RamDiscardManager

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Although RamDiscardManager can handle running into the maximum number of
DMA mappings by propagating errors when creating a DMA mapping, we want
to sanity check and warn the user early that there is a theoretical setup
issue and that virtio-mem might not be able to provide as much memory
towards a VM as desired.

As suggested by Alex, let's use the number of KVM memory slots to guess
how many other mappings we might see over time.

Acked-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Auger Eric <eric.auger@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: teawater <teawaterz@linux.alibaba.com>
Cc: Marek Kedzierski <mkedzier@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210413095531.25603-9-david@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
This commit is contained in:
David Hildenbrand 2021-04-13 11:55:26 +02:00 committed by Eduardo Habkost
parent 3eed155caf
commit a74317f636
1 changed files with 43 additions and 0 deletions
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43
hw/vfio/common.c
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@ -728,6 +728,49 @@ static void vfio_register_ram_discard_listener(VFIOContainer *container,
vfio_ram_discard_notify_discard, true);
ram_discard_manager_register_listener(rdm, &vrdl->listener, section);
QLIST_INSERT_HEAD(&container->vrdl_list, vrdl, next);
/*
* Sanity-check if we have a theoretically problematic setup where we could
* exceed the maximum number of possible DMA mappings over time. We assume
* that each mapped section in the same address space as a RamDiscardManager
* section consumes exactly one DMA mapping, with the exception of
* RamDiscardManager sections; i.e., we don't expect to have gIOMMU sections
* in the same address space as RamDiscardManager sections.
*
* We assume that each section in the address space consumes one memslot.
* We take the number of KVM memory slots as a best guess for the maximum
* number of sections in the address space we could have over time,
* also consuming DMA mappings.
*/
if (container->dma_max_mappings) {
unsigned int vrdl_count = 0, vrdl_mappings = 0, max_memslots = 512;
#ifdef CONFIG_KVM
if (kvm_enabled()) {
max_memslots = kvm_get_max_memslots();
}
#endif
QLIST_FOREACH(vrdl, &container->vrdl_list, next) {
hwaddr start, end;
start = QEMU_ALIGN_DOWN(vrdl->offset_within_address_space,
vrdl->granularity);
end = ROUND_UP(vrdl->offset_within_address_space + vrdl->size,
vrdl->granularity);
vrdl_mappings += (end - start) / vrdl->granularity;
vrdl_count++;
}
if (vrdl_mappings + max_memslots - vrdl_count >
container->dma_max_mappings) {
warn_report("%s: possibly running out of DMA mappings. E.g., try"
" increasing the 'block-size' of virtio-mem devies."
" Maximum possible DMA mappings: %d, Maximum possible"
" memslots: %d", __func__, container->dma_max_mappings,
max_memslots);
}
}
}
static void vfio_unregister_ram_discard_listener(VFIOContainer *container,