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authorChristoffer Dall <cdall@linaro.org>2017-03-21 22:05:22 +0100
committerChristoffer Dall <cdall@linaro.org>2017-04-04 14:33:59 +0200
commit6d56111c92d247bb64301029fe88365aa4caf16e (patch)
tree0ceec9bfeae39452c020baa35b99f91d9e4bae76 /Documentation
parent5b0d2cc2805897c14257f6dbb949639c499c3c25 (diff)
downloadlinux-6d56111c92d247bb64301029fe88365aa4caf16e.tar.bz2
KVM: arm/arm64: vgic: Fix GICC_PMR uaccess on GICv3 and clarify ABI
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. Reviewed-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Christoffer Dall <cdall@linaro.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/virtual/kvm/devices/arm-vgic.txt6
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/virtual/kvm/devices/arm-vgic.txt b/Documentation/virtual/kvm/devices/arm-vgic.txt
index 76e61c883347..b2f60ca8b60c 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.