On Tue, Mar 10, 2020 at 04:11:28PM -0500, Michael Roth wrote:
> The h_cede_tm kvm-unit-test currently fails when run inside an L1 guest
> via the guest/nested hypervisor.
>
> ./run-tests.sh -v
> ...
> TESTNAME=h_cede_tm TIMEOUT=90s ACCEL= ./powerpc/run powerpc/tm.elf -smp 2,threads=2 -machine cap-htm=on -append "h_cede_tm"
> FAIL h_cede_tm (2 tests, 1 unexpected failures)
>
> While the test relates to transactional memory instructions, the actual
> failure is due to the return code of the H_CEDE hypercall, which is
> reported as 224 instead of 0. This happens even when no TM instructions
> are issued.
>
> 224 is the value placed in r3 to execute a hypercall for H_CEDE, and r3
> is where the caller expects the return code to be placed upon return.
>
> In the case of guest running under a nested hypervisor, issuing H_CEDE
> causes a return from H_ENTER_NESTED. In this case H_CEDE is
> specially-handled immediately rather than later in
> kvmppc_pseries_do_hcall() as with most other hcalls, but we forget to
> set the return code for the caller, hence why kvm-unit-test sees the
> 224 return code and reports an error.
>
> Guest kernels generally don't check the return value of H_CEDE, so
> that likely explains why this hasn't caused issues outside of
> kvm-unit-tests so far.
>
> Fix this by setting r3 to 0 after we finish processing the H_CEDE.
>
> RHBZ: 1778556
>
> Fixes: 4bad77799fed ("KVM: PPC: Book3S HV: Handle hypercalls correctly when nested")
> Cc: linuxppc-dev@xxxxxxxxxx
> Cc: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxxx>
> Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
Thanks, applied to my kvm-ppc-next branch.
Paul.
