Commit ff42df49 authored by Paul Mackerras's avatar Paul Mackerras
Browse files

KVM: PPC: Book3S HV: Don't lose pending doorbell request on migration on P9 



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
interrupt.

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: stable@vger.kernel.org # v4.13+
Fixes: 57900694 ("KVM: PPC: Book3S HV: Virtualize doorbell facility on POWER9")
Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
Tested-by: default avatarAlexey Kardashevskiy <aik@ozlabs.ru>
parent d28eafc5

arch/powerpc/kvm/book3s_hv.c

+8 −1
Original line number Diff line number Diff line
@@ -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);

		break;

	case KVM_REG_PPC_DPDES:

		*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);

		break;

	case KVM_REG_PPC_VTB:

		*val = get_reg_val(id, vcpu->arch.vcore->vtb);