linux-kernel - [PATCH] KVM: arm/arm64: vgic: Handle GICR

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Date:   Fri, 20 Dec 2019 19:18:33 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     <maz@...nel.org>
CC:     <andre.przywara@....com>, <eric.auger@...hat.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>, <linux-kernel@...r.kernel.org>,
        <wanghaibin.wang@...wei.com>, Zenghui Yu <yuzenghui@...wei.com>
Subject: [PATCH] KVM: arm/arm64: vgic: Handle GICR_PENDBASER.PTZ filed as RAZ

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@...wei.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,
-- 
2.19.1