On 2022/12/01 19:40, Peter Maydell wrote:
On Thu, 1 Dec 2022 at 10:27, Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote:
A register access error typically means something seriously wrong
happened so that anything bad can happen after that and recovery is
impossible.
Even failing one register access is catastorophic as
architecture-specific code are not written so that it torelates such
failures.
Make sure the VM stop and nothing worse happens if such an error occurs.
Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>
In a similar vein there was also
https://lore.kernel.org/all/20220617144857.34189-1-peterx@xxxxxxxxxx/
back in June, which on the one hand was less comprehensive but on
the other does the plumbing to pass the error upwards rather than
reporting it immediately at point of failure.
I'm in principle in favour but suspect we'll run into some corner
cases where we were happily ignoring not-very-important failures
(eg if you're running Linux as the host OS on a Mac M1 and your
host kernel doesn't have this fix:
https://lore.kernel.org/all/YnHz6Cw5ONR2e+KA@xxxxxxxxxx/T/
then QEMU will go from "works by sheer luck" to "consistently
hits this error check"). So we should aim to land this extra
error checking early in the release cycle so we have plenty of
time to deal with any bug reports we get about it.
thanks
-- PMM
Actually I found this problem when I tried to run QEMU with KVM on M2
MacBook Air and encountered a failure described and fixed at:
https://lore.kernel.org/all/20221201104914.28944-2-akihiko.odaki@xxxxxxxxxx/
Although the affected register was not really important, QEMU couldn't
run the guest well enough because kvm_arch_put_registers for ARM64 is
written in a way that it fails early. I guess the situation is not so
different for other architectures as well.
I still agree that this should be postponed until a new release cycle
starts as register saving/restoring is too important to fail.
Regards,
Akihiko Odaki
