KVM: SEV: Add helper function to pin/unpin a single page

Add helpers to pin/unpin a single page, and use it in all flows that pin
exactly one page.  None of the single-page users actually check that the
correct number of pages was pinned, which is functionally ok, but visually
jarring, especially in the decrypt/encrypt flow, which separately pins two
pages, but uses a single variable to track how pages were pinned each time.
Again, it's functionally ok since core mm guarantees exactly one page will
be pinned on success, but it's ugly.

Opportunistically use page_to_phys() instead of open coding an equivalent
via page_to_pfn().

Note, all users of the single-page helper pre-validate the address and
length, i.e. don't rely on the sanity check in sev_pin_memory().

No functional change intended.

Link: https://patch.msgid.link/20260501203537.2120074-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

0 files changed, 0 insertions, 0 deletions