blob: 401c78c01c0b3f94837613043f7adda431842c80 [file] [log] [blame]
From de3918fc020ae25d914de1503b96aa7ee5f01f54 Mon Sep 17 00:00:00 2001
From: Paul Mackerras <>
Date: Tue, 27 Aug 2019 11:35:40 +1000
Subject: [PATCH] KVM: PPC: Book3S HV: Don't lose pending doorbell request on
migration on P9
commit ff42df49e75f053a8a6b4c2533100cdcc23afe69 upstream.
On POWER9, when userspace reads the value of the DPDES register on a
vCPU, it is possible for 0 to be returned although there is a doorbell
interrupt pending for the vCPU. This can lead to a doorbell interrupt
being lost across migration. If the guest kernel uses doorbell
interrupts for IPIs, then it could malfunction because of the lost
This happens because a newly-generated doorbell interrupt is signalled
by setting vcpu->arch.doorbell_request to 1; the DPDES value in
vcpu->arch.vcore->dpdes is not updated, because it can only be updated
when holding the vcpu mutex, in order to avoid races.
To fix this, we OR in vcpu->arch.doorbell_request when reading the
DPDES value.
Cc: # v4.13+
Fixes: 579006944e0d ("KVM: PPC: Book3S HV: Virtualize doorbell facility on POWER9")
Signed-off-by: Paul Mackerras <>
Tested-by: Alexey Kardashevskiy <>
Signed-off-by: Paul Gortmaker <>
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 36d72e9faddf..f8975c620f41 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1678,7 +1678,14 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
*val = get_reg_val(id, vcpu->arch.pspb);
- *val = get_reg_val(id, vcpu->arch.vcore->dpdes);
+ /*
+ * On POWER9, where we are emulating msgsndp etc.,
+ * we return 1 bit for each vcpu, which can come from
+ * either vcore->dpdes or doorbell_request.
+ * On POWER8, doorbell_request is 0.
+ */
+ *val = get_reg_val(id, vcpu->arch.vcore->dpdes |
+ vcpu->arch.doorbell_request);
*val = get_reg_val(id, vcpu->arch.vcore->vtb);