google / alioth / 43391685377

44%

push

github

fix(virtio/pci): clear driver features and selectors on device reset

Upon a device or PCI reset, VirtioPciRegisterMmio::complete_reset cleared
MSI-X vectors, queue registers, and device_status, but left
driver_feature[0..4], device_feature_sel, driver_feature_sel, and
queue_sel retaining their values from the previous driver instance.

Per VirtIO 1.4 Sec 2.2, resetting the device is the only way to
renegotiate features, so the features accepted by the previous driver
must not survive a reset. Otherwise a driver that writes fewer feature
banks than the previous one, e.g. EDK2 or Linux before v6.17 (banks 0
and 1) after Linux v6.17 or later (banks 0 to 3), starts the device
with stale bits 64 to 127. Current guests are not affected: no device
offers bits above 63 yet, and Linux and EDK2 rewrite banks 0 and 1
after a reset.

Clear all driver_feature banks and selector registers with Release
ordering before clearing device_status, so that a reset returns every
driver-writable register of the common configuration to its initial
value.

Fixes: 438fcfda5de2 ("feat(virtio/pci): handle device status init/reset")
Signed-off-by: Changyuan Lyu <changyuanl@google.com>

994 of 1776 branches covered (55.97%)

Branch coverage included in aggregate %.

5 of 5 new or added lines in 1 file covered. (100.0%)

7080 of 16557 relevant lines covered (42.76%)

900.54 hits per line