amd_iommu: Return an error when unable to read PTE from guest memory

Make amdvi_get_pte_entry() return an error value (-1) in cases where the
memory read fails, versus the current return of 0 to indicate failure.
The reason is that 0 is also a valid value to have stored in the PTE in
guest memory i.e. the guest does not have a mapping. Before this change,
amdvi_get_pte_entry() returned 0 for both an error and for empty PTEs, but
the page walker implementation that will be introduced in upcoming changes
needs a method to differentiate between the two scenarios.

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20250919213515.917111-7-alejandro.j.jimenez@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
1 file changed