Messages in this thread | | | Date | Tue, 27 Sep 2022 10:35:42 +0200 | Subject | Re: [RFC PATCH 9/9] kvm_main.c: handle atomic memslot update | From | Emanuele Giuseppe Esposito <> |
| |
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
What guest sees: memslot X is invalid, so MMU keeps retrying the page fault
Third pass: swap() // 1 for each address space affected
What guest sees: new memslot replacing the old one
A split is DELETE+CREATE+CREATE, so it's the same:
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: delete old memslot X create new memslot X1 create new memslot X2
What guest sees: memslot X is invalid, so MMU keeps retrying the page fault
Third pass: swap() // 1 for each address space affected
What guest sees: two new memslots replacing the old one
| |