KVM: Add transparent hugepage support for dedicated guest memory
Extended guest_memfd to allow backing guest memory with transparent
hugepages. Require userspace to opt-in via a flag even though there's no
known/anticipated use case for forcing small pages as THP is optional,
i.e. to avoid ending up in a situation where userspace is unaware that
KVM can't provide hugepages.
For simplicity, require the guest_memfd size to be a multiple of the
hugepage size, e.g. so that KVM doesn't need to do bounds checking when
deciding whether or not to allocate a huge folio.
When reporting the max order when KVM gets a pfn from guest_memfd, force
order-0 pages if the hugepage is not fully contained by the memslot
binding, e.g. if userspace requested hugepages but punches a hole in the
memslot bindings in order to emulate x86's VGA hole.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20231027182217.3615211-18-seanjc@google.com>
[Allow even with CONFIG_TRANSPARENT_HUGEPAGE; dropped momentarily due to
uneasiness about the API. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
6 files changed
