From: Michael Roth mdroth@linux.vnet.ibm.com
[ Upstream commit 1f50cc1705350a4697923203fedd7d8fb1087fe2 ]
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@ozlabs.org Cc: David Gibson david@gibson.dropbear.id.au Cc: Paul Mackerras paulus@ozlabs.org Signed-off-by: Michael Roth mdroth@linux.vnet.ibm.com Reviewed-by: David Gibson david@gibson.dropbear.id.au Signed-off-by: Paul Mackerras paulus@ozlabs.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/kvm/book3s_hv.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 36abbe3c346df..e2183fed947d4 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -3623,6 +3623,7 @@ int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit, if (trap == BOOK3S_INTERRUPT_SYSCALL && !vcpu->arch.nested && kvmppc_get_gpr(vcpu, 3) == H_CEDE) { kvmppc_nested_cede(vcpu); + kvmppc_set_gpr(vcpu, 3, 0); trap = 0; } } else {