As an oversight, for GICv2, we accidentally export the GICC_PMR register
in the format of the GICH_VMCR.VMPriMask field in the lower 5 bits of a
word, meaning that userspace must always use the lower 5 bits to
communicate with the KVM device and must shift the value left by 3
places to obtain the actual priority mask level.
Since GICv3 supports the full 8 bits of priority masking in the ICH_VMCR,
we have to fix the value we export when emulating a GICv2 on top of a
hardware GICv3 and exporting the emulated GICv2 state to userspace.
Take the chance to clarify this aspect of the ABI.
Signed-off-by: Christoffer Dall <cdall@xxxxxxxxxx>
---
Documentation/virtual/kvm/devices/arm-vgic.txt | 6 ++++++
include/linux/irqchip/arm-gic.h | 3 +++
virt/kvm/arm/vgic/vgic-mmio-v2.c | 20 ++++++++++++++++++--
virt/kvm/arm/vgic/vgic-v2.c | 8 ++++----
virt/kvm/arm/vgic/vgic.h | 9 ++++++++-
5 files changed, 39 insertions(+), 7 deletions(-)
diff --git a/Documentation/virtual/kvm/devices/arm-vgic.txt b/Documentation/virtual/kvm/devices/arm-vgic.txt
index 76e61c8..b2f60ca 100644
--- a/Documentation/virtual/kvm/devices/arm-vgic.txt
+++ b/Documentation/virtual/kvm/devices/arm-vgic.txt
@@ -83,6 +83,12 @@ Groups:
Bits for undefined preemption levels are RAZ/WI.
+ For historical reasons and to provide ABI compatibility with userspace we
+ export the GICC_PMR register in the format of the GICH_VMCR.VMPriMask
+ field in the lower 5 bits of a word, meaning that userspace must always
+ use the lower 5 bits to communicate with the KVM device and must shift the
+ value left by 3 places to obtain the actual priority mask level.
+
Limitations:
- Priorities are not implemented, and registers are RAZ/WI
- Currently only implemented for KVM_DEV_TYPE_ARM_VGIC_V2.
diff --git a/include/linux/irqchip/arm-gic.h b/include/linux/irqchip/arm-gic.h
index eafc965..dc30f3d 100644
--- a/include/linux/irqchip/arm-gic.h
+++ b/include/linux/irqchip/arm-gic.h
@@ -96,6 +96,9 @@
#define GICH_MISR_EOI (1 << 0)
#define GICH_MISR_U (1 << 1)
+#define GICV_PMR_PRIORITY_SHIFT 3
+#define GICV_PMR_PRIORITY_MASK (0x1f << GICV_PMR_PRIORITY_SHIFT)
+
#ifndef __ASSEMBLY__
#include <linux/irqdomain.h>
diff --git a/virt/kvm/arm/vgic/vgic-mmio-v2.c b/virt/kvm/arm/vgic/vgic-mmio-v2.c
index a3ad7ff..0a4283e 100644
--- a/virt/kvm/arm/vgic/vgic-mmio-v2.c
+++ b/virt/kvm/arm/vgic/vgic-mmio-v2.c
@@ -229,7 +229,15 @@ static unsigned long vgic_mmio_read_vcpuif(struct kvm_vcpu *vcpu,
val = vmcr.ctlr;
break;
case GIC_CPU_PRIMASK:
- val = vmcr.pmr;
+ /*
+ * Our KVM_DEV_TYPE_ARM_VGIC_V2 device ABI exports the
+ * the PMR field as GICH_VMCR.VMPriMask rather than
+ * GICC_PMR.Priority, so we expose the upper five bits of
+ * priority mask to userspace using the lower bits in the
+ * unsigned long.
+ */
+ val = (vmcr.pmr & GICV_PMR_PRIORITY_MASK) >>
+ GICV_PMR_PRIORITY_SHIFT;
break;
case GIC_CPU_BINPOINT:
val = vmcr.bpr;
@@ -262,7 +270,15 @@ static void vgic_mmio_write_vcpuif(struct kvm_vcpu *vcpu,
vmcr.ctlr = val;
break;
case GIC_CPU_PRIMASK:
- vmcr.pmr = val;
+ /*
+ * Our KVM_DEV_TYPE_ARM_VGIC_V2 device ABI exports the
+ * the PMR field as GICH_VMCR.VMPriMask rather than
+ * GICC_PMR.Priority, so we expose the upper five bits of
+ * priority mask to userspace using the lower bits in the
+ * unsigned long.
+ */
+ vmcr.pmr = (val << GICV_PMR_PRIORITY_SHIFT) &
+ GICV_PMR_PRIORITY_MASK;
break;
case GIC_CPU_BINPOINT:
vmcr.bpr = val;
diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c
index b834ecd..955f24c 100644
--- a/virt/kvm/arm/vgic/vgic-v2.c
+++ b/virt/kvm/arm/vgic/vgic-v2.c
@@ -191,8 +191,8 @@ void vgic_v2_set_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
GICH_VMCR_ALIAS_BINPOINT_MASK;
vmcr |= (vmcrp->bpr << GICH_VMCR_BINPOINT_SHIFT) &
GICH_VMCR_BINPOINT_MASK;
- vmcr |= (vmcrp->pmr << GICH_VMCR_PRIMASK_SHIFT) &
- GICH_VMCR_PRIMASK_MASK;
+ vmcr |= ((vmcrp->pmr >> GICV_PMR_PRIORITY_SHIFT) <<
+ GICH_VMCR_PRIMASK_SHIFT) & GICH_VMCR_PRIMASK_MASK;
vcpu->arch.vgic_cpu.vgic_v2.vgic_vmcr = vmcr;
}
@@ -207,8 +207,8 @@ void vgic_v2_get_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
GICH_VMCR_ALIAS_BINPOINT_SHIFT;
vmcrp->bpr = (vmcr & GICH_VMCR_BINPOINT_MASK) >>
GICH_VMCR_BINPOINT_SHIFT;
- vmcrp->pmr = (vmcr & GICH_VMCR_PRIMASK_MASK) >>
- GICH_VMCR_PRIMASK_SHIFT;
+ vmcrp->pmr = ((vmcr & GICH_VMCR_PRIMASK_MASK) >>
+ GICH_VMCR_PRIMASK_SHIFT) << GICV_PMR_PRIORITY_SHIFT;
}
void vgic_v2_enable(struct kvm_vcpu *vcpu)
diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
index db28f7c..1d8cb65 100644
--- a/virt/kvm/arm/vgic/vgic.h
+++ b/virt/kvm/arm/vgic/vgic.h
@@ -81,11 +81,18 @@ static inline bool irq_is_pending(struct vgic_irq *irq)
return irq->pending_latch || irq->line_level;
}
+/*
+ * This struct provides an intermediate representation of the fields contained
+ * in the GICH_VMCR and ICH_VMCR registers, such that code exporting the GIC
+ * state to userspace can generate either GICv2 or GICv3 CPU interface
+ * registers regardless of the hardware backed GIC used.
+ */
struct vgic_vmcr {
u32 ctlr;
u32 abpr;
u32 bpr;
- u32 pmr;
+ u32 pmr; /* Priority mask field in the GICC_PMR and
+ * ICC_PMR_EL1 priority field format */
/* Below member variable are valid only for GICv3 */
u32 grpen0;
u32 grpen1;
--
2.9.0
