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Date: Thu, 06 Jun 2024 12:59:47 +1000
Message-Id: <D1SLJVD2W76U.3974CEMY2E585@gmail.com>
Cc: <linuxppc-dev@lists.ozlabs.org>, <linux-doc@vger.kernel.org>,
 <kvm@vger.kernel.org>, <stable@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] arch/powerpc/kvm: Fix doorbell emulation for v2
 API
From: "Nicholas Piggin" <npiggin@gmail.com>
To: "Gautam Menghani" <gautam@linux.ibm.com>, <mpe@ellerman.id.au>,
 <christophe.leroy@csgroup.eu>, <aneesh.kumar@kernel.org>,
 <naveen.n.rao@linux.ibm.com>, <corbet@lwn.net>
References: <20240605113913.83715-1-gautam@linux.ibm.com>
 <20240605113913.83715-3-gautam@linux.ibm.com>
In-Reply-To: <20240605113913.83715-3-gautam@linux.ibm.com>

On Wed Jun 5, 2024 at 9:39 PM AEST, Gautam Menghani wrote:
> 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 XI=
CS
> (pSeries_smp_probe()).
>
> Command to replicate the above bug:
>
> qemu-system-ppc64 \
> 	-drive file=3Drhel.qcow2,format=3Dqcow2 \
> 	-m 20G \
> 	-smp 8,cores=3D1,threads=3D8 \
> 	-cpu  host \
> 	-nographic \
> 	-machine pseries,ic-mode=3Dxics -accel kvm
>
> Add doorbell state handling support in the host
> KVM code to fix doorbell emulation.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

>
> Fixes: 19d31c5f1157 ("KVM: PPC: Add support for nestedv2 guests")
> Cc: stable@vger.kernel.org # v6.7
> Signed-off-by: Gautam Menghani <gautam@linux.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_vc=
pu *vcpu, u64 time_limit,
>  	int trap;
>  	long rc;
> =20
> +	if (vcpu->arch.doorbell_request) {
> +		vcpu->arch.doorbell_request =3D 0;
> +		kvmppc_set_dpdes(vcpu, 1);
> +	}
> +
>  	io =3D &vcpu->arch.nestedv2_io;
> =20
>  	msr =3D mfmsr();