KVM: arm64: Use acquire/release to communicate FF-A version negotiation

The pKVM FF-A proxy rejects FF-A requests other than FFA_VERSION until
version negotiation is complete, which is signalled by setting the
global 'has_version_negotiated' variable.

To avoid excessive locking, this variable is checked directly from
kvm_host_ffa_handler() in response to an FF-A call, but this can race
against another CPU performing the negotiation and potentially lead to
reading a torn value (incredibly unlikely for a 'bool') or problematic
re-ordering of the accesses to 'has_version_negotiated' and
'hyp_ffa_version' whereby a stale version number could be read by
__do_ffa_mem_xfer().

Use acquire/release primitives when writing 'has_version_negotiated'
with the version lock held and when reading without the lock held.

Cc: Sebastian Ene <[email protected]>
Cc: Sudeep Holla <[email protected]>
Cc: Quentin Perret <[email protected]>
Cc: Oliver Upton <[email protected]>
Cc: Marc Zyngier <[email protected]>
Fixes: c9c012625e12 ("KVM: arm64: Trap FFA_VERSION host call in pKVM")
Signed-off-by: Will Deacon <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Oliver Upton <[email protected]>

0 files changed, 0 insertions, 0 deletions