This is a note to let you know that I've just added the patch titled
KVM: PPC: Book3S HV: Avoid returning to nested hypervisor on pending doorbells
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-ppc-book3s-hv-avoid-returning-to-nested-hypervis.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 18faaf580c5ba5d372b124e721811bbb3be28adf
Author: Gautam Menghani <gautam@xxxxxxxxxxxxx>
Date: Sat Nov 9 12:02:57 2024 +0530
KVM: PPC: Book3S HV: Avoid returning to nested hypervisor on pending doorbells
[ 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@xxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://patch.msgid.link/20241109063301.105289-4-gautam@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 479218389e7cd..45708ac55e90e 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4653,7 +4653,6 @@ 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;
