6.6-stable review patch. If anyone has any objections, please let me know.
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From: Gautam Menghani gautam@linux.ibm.com
[ Upstream commit 26686db69917399fa30e3b3135360771e90f83ec ]
Commit 6398326b9ba1 ("KVM: PPC: Book3S HV P9: Stop using vc->dpdes") dropped the use of vcore->dpdes for msgsndp / SMT emulation. Prior to that commit, the below code at L1 level (see [1] for terminology) was responsible for setting vc->dpdes for the respective L2 vCPU:
if (!nested) { kvmppc_core_prepare_to_enter(vcpu); if (vcpu->arch.doorbell_request) { vc->dpdes = 1; smp_wmb(); vcpu->arch.doorbell_request = 0; }
L1 then sent vc->dpdes to L0 via kvmhv_save_hv_regs(), and while servicing H_ENTER_NESTED at L0, the below condition at L0 level made sure to abort and go back to L1 if vcpu->arch.doorbell_request = 1 so that L1 sets vc->dpdes as per above if condition:
} else if (vcpu->arch.pending_exceptions || vcpu->arch.doorbell_request || xive_interrupt_pending(vcpu)) { vcpu->arch.ret = RESUME_HOST; goto out; }
This worked fine since vcpu->arch.doorbell_request was used more like a flag and vc->dpdes was used to pass around the doorbell state. But after Commit 6398326b9ba1 ("KVM: PPC: Book3S HV P9: Stop using vc->dpdes"), vcpu->arch.doorbell_request is the only variable used to pass around doorbell state. With the plumbing for handling doorbells for nested guests updated to use vcpu->arch.doorbell_request over vc->dpdes, the above "else if" stops doorbells from working correctly as L0 aborts execution of L2 and instead goes back to L1.
Remove vcpu->arch.doorbell_request from the above "else if" condition as it is no longer needed for L0 to correctly handle the doorbell status while running L2.
[1] Terminology 1. L0 : PowerNV linux running with HV privileges 2. L1 : Pseries KVM guest running on top of L0 2. L2 : Nested KVM guest running on top of L1
Fixes: 6398326b9ba1 ("KVM: PPC: Book3S HV P9: Stop using vc->dpdes") Signed-off-by: Gautam Menghani gautam@linux.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://patch.msgid.link/20241109063301.105289-4-gautam@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/kvm/book3s_hv.c | 1 - 1 file changed, 1 deletion(-)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 14511e457ade1..924689fa5efa1 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -4687,7 +4687,6 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit, lpcr |= LPCR_MER; } } else if (vcpu->arch.pending_exceptions || - vcpu->arch.doorbell_request || xive_interrupt_pending(vcpu)) { vcpu->arch.ret = RESUME_HOST; goto out;