Messages in this thread | | | Date | Tue, 27 Sep 2022 11:22:19 +0200 | Subject | Re: [RFC PATCH 9/9] kvm_main.c: handle atomic memslot update | From | David Hildenbrand <> |
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On 27.09.22 10:35, Emanuele Giuseppe Esposito wrote: > > > Am 27/09/2022 um 09:46 schrieb David Hildenbrand: >> On 09.09.22 12:45, Emanuele Giuseppe Esposito wrote: >>> When kvm_vm_ioctl_set_memory_region_list() is invoked, we need >>> to make sure that all memslots are updated in the inactive list >>> and then swap (preferreably only once) the lists, so that all >>> changes are visible immediately. >>> >>> The only issue is that DELETE and MOVE need to perform 2 swaps: >>> firstly replace old memslot with invalid, and then remove invalid. >>> >> >> I'm curious, how would a resize (grow/shrink) or a split be handled? >> > > There are only 4 operations possible in KVM: KVM_MR_{DELETE, MOVE, > CREATE, FLAGS_ONLY}. > > A resize should be implemented in QEMU as DELETE+CREATE. > > Therefore a resize on memslot X will be implemented as: > First pass on the userspace operations: > invalidate memslot X; > swap_memslot_list(); // NOW it is visible to the guest > > What guest sees: memslot X is invalid, so MMU keeps retrying the page fault > > Second pass: > create new memslot X > delete old memslot X
Thanks a lot for the very nice explanation!
Does the invalidation already free up memslot metadata (especially the rmaps) or will we end up temporarily allocating twice the memslot metadata?
-- Thanks,
David / dhildenb
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