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Subject: Re: [PATCH] KVM: arm/arm64: vgic: Handle GICR_PENDBASER.PTZ filed as
 RAZ
To:     Zenghui Yu <yuzenghui@huawei.com>, maz@kernel.org
Cc:     andre.przywara@arm.com, linux-kernel@vger.kernel.org,
        wanghaibin.wang@huawei.com, kvmarm@lists.cs.columbia.edu,
        linux-arm-kernel@lists.infradead.org
References: <20191220111833.1422-1-yuzenghui@huawei.com>
From:   Auger Eric <eric.auger@redhat.com>
Message-ID: <8f8b063c-45cf-166d-bd94-ff96831314c0@redhat.com>
Date:   Fri, 20 Dec 2019 13:18:40 +0100
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Hi Zenghui,

On 12/20/19 12:18 PM, Zenghui Yu wrote:
> Although guest will hardly read and use the PTZ (Pending Table Zero)
> bit in GICR_PENDBASER, let us emulate the architecture strictly.
> As per IHI 0069E 9.11.30, PTZ field is WO, and reads as 0.
> 
> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
> ---
> 
> Noticed when checking all fields of GICR_PENDBASER register.
> But _not_ sure whether it's worth a fix, as Linux never sets
> the PTZ bit before enabling LPI (set GICR_CTLR_ENABLE_LPIS).
> 
> And I wonder under which scenarios can this bit be written as 1.
> It seems difficult for software to determine whether the pending
> table contains all zeros when writing this bit.
> 
>  virt/kvm/arm/vgic/vgic-mmio-v3.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-mmio-v3.c b/virt/kvm/arm/vgic/vgic-mmio-v3.c
> index 7dfd15dbb308..ebc218840fc2 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-mmio-v3.c
> @@ -414,8 +414,11 @@ static unsigned long vgic_mmio_read_pendbase(struct kvm_vcpu *vcpu,
>  					     gpa_t addr, unsigned int len)
>  {
>  	struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> +	u64 value = vgic_cpu->pendbaser;
>  
> -	return extract_bytes(vgic_cpu->pendbaser, addr & 7, len);
> +	value &= ~GICR_PENDBASER_PTZ;
> +
> +	return extract_bytes(value, addr & 7, len);
>  }
>  
>  static void vgic_mmio_write_pendbase(struct kvm_vcpu *vcpu,
> 
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric