Explicitly flush caches after intra-host migration before clearing "SEV
active" on the source VM, as doing cache maintenance afterwards creates a
tiny window where memory reclaim could return memory to the host without
performing a cache flush, e.g. as pointed out by Sashiko:
CPU1 in sev_migrate_from():
src->active = false;
CPU2 running concurrent unmap:
Since active is false, the automatic cache flush in
sev_guest_memory_reclaimed is skipped.
The host frees and reallocates the page.
CPU1 in sev_migrate_from():
sev_writeback_caches(src_kvm);
Executes a hardware cache flush (wbnoinvd), which writes the guest's old
dirty ciphertext over the new page owner's data.
Fixes: 93de2a6a4b ("KVM: SEV: Do cache maintenance on the source VM during intra-host migration")
Cc: stable@vger.kernel.org
Reported-by: Sashiko Bot <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260923165304.1662E1F000FF@smtp.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260928154644.2559454-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
973ea70393