On 14.01.21 00:34, Alex Williamson wrote:
> On Thu, 7 Jan 2021 14:34:18 +0100
> David Hildenbrand <da...@redhat.com> wrote:
>
>> Although RamDiscardMgr 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.
>>
>> 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 | 43 +++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 43 insertions(+)
>>
>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>> index 1babb6bb99..bc20f738ce 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -758,6 +758,49 @@ static void
>> vfio_register_ram_discard_notifier(VFIOContainer *container,
>> vfio_ram_discard_notify_discard_all);
>> rdmc->register_listener(rdm, section->mr, &vrdl->listener);
>> 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 RamDiscardMgr
>> + * section consumes exactly one DMA mapping, with the exception of
>> + * RamDiscardMgr sections; i.e., we don't expect to have gIOMMU
>> sections in
>> + * the same address space as RamDiscardMgr 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;
>
> ---> += ?
Ah, yes, thanks. That's the result of testing only with a single
virtio-mem device :)
--
Thanks,
David / dhildenb
