Re: [PATCH] KVM: PPC: Book3S HV: Fix H_CEDE return code for nested guests
From: David Gibson <hidden>
Date: 2020-03-10 23:17:09
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@ozlabs.org
Cc: David Gibson <redacted>
Cc: Paul Mackerras <redacted>
Signed-off-by: Michael Roth <redacted>Reviewed-by: David Gibson <redacted>
quoted hunk ↗ jump to hunk
--- 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 2cefd071b848..c0c43a733830 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c@@ -3616,6 +3616,7 @@ 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 {
-- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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