linux-kernel - [PATCH v2 2/2] arch/powerpc/kvm: Fix doorbell emulation for v2 API

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Message-ID: <20240605113913.83715-3-gautam@linux.ibm.com>
Date: Wed,  5 Jun 2024 17:09:10 +0530
From: Gautam Menghani <gautam@...ux.ibm.com>
To: mpe@...erman.id.au, npiggin@...il.com, christophe.leroy@...roup.eu,
        aneesh.kumar@...nel.org, naveen.n.rao@...ux.ibm.com, corbet@....net
Cc: Gautam Menghani <gautam@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-doc@...r.kernel.org, kvm@...r.kernel.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] arch/powerpc/kvm: Fix doorbell emulation for v2 API

Doorbell emulation is broken for KVM on PAPR guests as support for
DPDES was not added in the initial patch series. Due to this, a KVM on
PAPR guest with SMT > 1 cannot be booted with the XICS interrupt
controller as doorbells are setup in the initial probe path when using XICS
(pSeries_smp_probe()).

Command to replicate the above bug:

qemu-system-ppc64 \
	-drive file=rhel.qcow2,format=qcow2 \
	-m 20G \
	-smp 8,cores=1,threads=8 \
	-cpu  host \
	-nographic \
	-machine pseries,ic-mode=xics -accel kvm

Add doorbell state handling support in the host
KVM code to fix doorbell emulation.

Fixes: 19d31c5f1157 ("KVM: PPC: Add support for nestedv2 guests")
Cc: stable@...r.kernel.org # v6.7
Signed-off-by: Gautam Menghani <gautam@...ux.ibm.com>
---
 arch/powerpc/kvm/book3s_hv.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 35cb014a0c51..21c69647d27c 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4116,6 +4116,11 @@ static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu *vcpu, u64 time_limit,
 	int trap;
 	long rc;
 
+	if (vcpu->arch.doorbell_request) {
+		vcpu->arch.doorbell_request = 0;
+		kvmppc_set_dpdes(vcpu, 1);
+	}
+
 	io = &vcpu->arch.nestedv2_io;
 
 	msr = mfmsr();
-- 
2.45.1