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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1ijO0G-0005nM-Hq; Mon, 23 Dec 2019 13:44:08 +0000 Received: from szxga06-in.huawei.com ([45.249.212.32] helo=huawei.com) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1ijO0D-0005mL-1V for linux-arm-kernel@lists.infradead.org; Mon, 23 Dec 2019 13:44:06 +0000 Received: from DGGEMS404-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 1E959C499F930DB2F9D9; Mon, 23 Dec 2019 21:43:54 +0800 (CST) Received: from [127.0.0.1] (10.173.222.27) by DGGEMS404-HUB.china.huawei.com (10.3.19.204) with Microsoft SMTP Server id 14.3.439.0; Mon, 23 Dec 2019 21:43:44 +0800 Subject: Re: [PATCH] KVM: arm/arm64: vgic: Handle GICR_PENDBASER.PTZ filed as RAZ To: References: <20191220111833.1422-1-yuzenghui@huawei.com> From: Zenghui Yu Message-ID: <3a729559-d0eb-e042-d6bd-b69bacb0dd23@huawei.com> Date: Mon, 23 Dec 2019 21:43:42 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: <20191220111833.1422-1-yuzenghui@huawei.com> Content-Language: en-US X-Originating-IP: [10.173.222.27] X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191223_054405_252663_008885CC X-CRM114-Status: GOOD ( 16.33 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: andre.przywara@arm.com, linux-kernel@vger.kernel.org, eric.auger@redhat.com, wanghaibin.wang@huawei.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2019/12/20 19:18, 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 > --- > > 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, > I noticed there is no userspace access callbacks for GICR_PENDBASER, so this patch will make the PTZ field also 'Read As Zero' by userspace. Should we consider adding a uaccess_read callback for GICR_PENDBASER which just returns the unchanged vgic_cpu->pendbaser to userspace? (Though this is really not a big deal. We now always emulate the PTZ field to guest as RAZ. And 'vgic_cpu->pendbaser & GICR_PENDBASER_PTZ' only indicates whether KVM will optimize the LPI enabling process, where Read As Zero indicates never optimize..) Thanks, Zenghui _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel