On 3/3/22 20:38, Paolo Bonzini wrote:
From: Sean Christopherson<seanjc@xxxxxxxxxx> Add a selftest that enables populating a VM with the maximum amount of guest memory allowed by the underlying architecture. Abuse KVM's memslots by mapping a single host memory region into multiple memslots so that the selftest doesn't require a system with terabytes of RAM. Default to 512gb of guest memory, which isn't all that interesting, but should work on all MMUs and doesn't take an exorbitant amount of memory or time. E.g. testing with ~64tb of guest memory takes the better part of an hour, and requires 200gb of memory for KVM's page tables when using 4kb pages.
I couldn't quite run this on a laptop, so I'll tune it down to 128gb and 3/4 of the available CPUs.
To inflicit maximum abuse on KVM' MMU, default to 4kb pages (or whatever the not-hugepage size is) in the backing store (memfd). Use memfd for the host backing store to ensure that hugepages are guaranteed when requested, and to give the user explicit control of the size of hugepage being tested. By default, spin up as many vCPUs as there are available to the selftest, and distribute the work of dirtying each 4kb chunk of memory across all vCPUs. Dirtying guest memory forces KVM to populate its page tables, and also forces KVM to write back accessed/dirty information to struct page when the guest memory is freed. On x86, perform two passes with a MMU context reset between each pass to coerce KVM into dropping all references to the MMU root, e.g. to emulate a vCPU dropping the last reference. Perform both passes and all rendezvous on all architectures in the hope that arm64 and s390x can gain similar shenanigans in the future.
Did you actually test aarch64 (not even asking about s390 :))? For now let's only add it for x86.
+ TEST_ASSERT(nr_vcpus, "#DE");
srsly? :) Paolo
