Am 08.03.22 um 15:47 schrieb Paolo Bonzini:
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.
I do get spurious
# selftests: kvm: max_guest_memory_test
# ==== Test Assertion Failure ====
# lib/kvm_util.c:883: !ret
# pid=575178 tid=575178 errno=22 - Invalid argument
# 1 0x000000000100385f: vm_set_user_memory_region at kvm_util.c:883
# 2 0x0000000001001ee1: main at max_guest_memory_test.c:242
# 3 0x000003ffa1033731: ?? ??:0
# 4 0x000003ffa103380d: ?? ??:0
# 5 0x0000000001002389: _start at ??:?
# KVM_SET_USER_MEMORY_REGION failed, errno = 22 (Invalid argument)
not ok 9 selftests: kvm: max_guest_memory_test # exit=254
as the userspace address must be 1MB-aligned but the mmap is not (due to aslr).
There are probably more issues, so it certainly is ok to skip s390 for now.
+ TEST_ASSERT(nr_vcpus, "#DE");
srsly? :)
Paolo
