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| author | Oliver Upton <oliver.upton@linux.dev> | 2025-07-23 23:28:05 -0700 |
|---|---|---|
| committer | Oliver Upton <oliver.upton@linux.dev> | 2025-07-26 08:45:52 -0700 |
| commit | eed9b14209073c51a0e41365871da05b1ada578f (patch) | |
| tree | 3c77ad18f7070d2d77e74cdc7316c8cef41d33ad | |
| parent | 15b5964a411f386d53e41a5595a3dd5e6068a59e (diff) | |
Documentation: KVM: arm64: Describe VGICv3 registers writable pre-init
KVM allows userspace to control GICD_IIDR.Revision and
GICD_TYPER2.nASSGIcap prior to initialization for the sake of
provisioning the guest-visible feature set. Document the userspace
expectations surrounding accesses to these registers.
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250724062805.2658919-7-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
| -rw-r--r-- | Documentation/virt/kvm/devices/arm-vgic-v3.rst | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/Documentation/virt/kvm/devices/arm-vgic-v3.rst b/Documentation/virt/kvm/devices/arm-vgic-v3.rst index e860498b1e35..c7a1cd22d814 100644 --- a/Documentation/virt/kvm/devices/arm-vgic-v3.rst +++ b/Documentation/virt/kvm/devices/arm-vgic-v3.rst @@ -78,6 +78,8 @@ Groups: -ENXIO The group or attribute is unknown/unsupported for this device or hardware support is missing. -EFAULT Invalid user pointer for attr->addr. + -EBUSY Attempt to write a register that is read-only after + initialization ======= ============================================================= @@ -120,6 +122,15 @@ Groups: Note that distributor fields are not banked, but return the same value regardless of the mpidr used to access the register. + Userspace is allowed to write the following register fields prior to + initialization of the VGIC: + + ===================== + GICD_IIDR.Revision + GICD_TYPER2.nASSGIcap + ===================== + + GICD_IIDR.Revision is updated when the KVM implementation is changed in a way directly observable by the guest or userspace. Userspace should read GICD_IIDR from KVM and write back the read value to confirm its expected @@ -128,6 +139,12 @@ Groups: behavior. + GICD_TYPER2.nASSGIcap allows userspace to control the support of SGIs + without an active state. At VGIC creation the field resets to the + maximum capability of the system. Userspace is expected to read the field + to determine the supported value(s) before writing to the field. + + The GICD_STATUSR and GICR_STATUSR registers are architecturally defined such that a write of a clear bit has no effect, whereas a write with a set bit clears that value. To allow userspace to freely set the values of these two |