amd_iommu: Fix pte_override_page_mask()

amd_iommu: Fix pte_override_page_mask()

AMD IOMMU PTEs have a special mode allowing to specify an arbitrary page
size. Quoting the AMD IOMMU specification: "When the Next Level bits [of
a pte] are 7h, the size of the page is determined by the first zero bit
in the page address, starting from bit 12."

So if the lowest bits of the page address is 0, the page is 8kB. If the
lowest bits are 011, the page is 32kB. Currently pte_override_page_mask()
doesn't compute the right value for this page size and amdvi_translate()
can return the wrong guest-physical address. With a Linux guest, DMA
from SATA devices accesses the wrong memory and causes probe failure:

qemu-system-x86_64 ... -device amd-iommu -drive id=hd1,file=foo.bin,if=none \
		-device ahci,id=ahci -device ide-hd,drive=hd1,bus=ahci.0
[    6.613093] ata1.00: qc timeout (cmd 0xec)
[    6.615062] ata1.00: failed to IDENTIFY (I/O error, err_mask=0x4)

Fix the page mask.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Message-Id: <20210421084007.1190546-1-jean-philippe@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>