KVM: guest_memfd: Call arch make_shared callback for to-shared conversion

When doing in-place conversion from PRIVATE to SHARED, immediately inform
arch code of the conversion for all allocated pages/folios, e.g. so that
arch code can put hardware metadata tables in the correct state.  Eagerly
updating the table for to SHARED conversions avoids having to implement
on-demand updates, e.g. when faulting in host userspace mappings.  Skip the
entire flow if the arch doesn't implement conversion callbacks, as getting
folios from the filemap is noticeably expensive, especially when converting
large chunks of memory.

Deliberately don't eagerly update the metadata table on conversions from
SHARED to PRIVATE, because assigning a page to a VM (versus "returning" it
to the host) requires the exact GFN associated with the page, i.e would
require walking the memslot bindings.  And because KVM *must* do on-demand
metadata updates when getting a PFN for KVM-internal usage, as that's the
only time a relevant memslot binding is guaranteed to exist.

Note!  Inform arch code of the conversion within the protection of the
invalidation sequence, to ensure that any existing mappings are dropped
before hardware is updated, and to ensure that new mappings can't be
established until after the conversion is complete.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Link: https://patch.msgid.link/20260910-gmem-inplace-conversion-v13-16-dd6fbf94f4e1@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

0 files changed, 0 insertions, 0 deletions