On Mon, Aug 12, 2024 at 02:12:29PM +0000, Wang, Wei W wrote: > In the example above, both UFFDIO_COPY and KVM_USERFAULT_COPY need to be > invoked, e.g.: > #1 invoke KVM_USERFAULT_COPY > #2 invoke UFFDIO_COPY > > This requires that UFFDIO_COPY does not conflict with KVM_USERFAULT_COPY. Current > UFFDIO_COPY will fail (thus not waking up the threads on the waitq) when it fails to > install the PTE into the page table (in the above example the PTE has already been > installed into the page table by KVM_USERFAULT_COPY at #1). Indeed, maybe we can fix that with an explicit UFFDIO_WAKE upon UFFDIO_COPY failures iff -EEXIST (in this case, it should fall into "page cache exists" category, even if pgtable can still be missing). I assume OTOH a racy KVM_USERFAULT_COPY in whatever form doesn't need anything but to kick the vcpu, irrelevant of whether the copy succeeded or not. Thanks, -- Peter Xu
