* [PATCH 5.6 076/166] KVM: PPC: Book3S HV: Fix H_CEDE return code for nested guests
[not found] <20200422095047.669225321@linuxfoundation.org>
@ 2020-04-22 9:56 ` Greg Kroah-Hartman
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From: Greg Kroah-Hartman @ 2020-04-22 9:56 UTC (permalink / raw)
To: linux-kernel
Cc: Sasha Levin, Greg Kroah-Hartman, Michael Roth, stable,
linuxppc-dev, David Gibson
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 2cefd071b8483..c0c43a7338304 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 {
--
2.20.1
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