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arm/arm64: KVM: vgic: Clarify and correct vgic documentation

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The VGIC virtual distributor implementation documentation was written a
very long time ago, before the true nature of the beast had been
partially absorbed into my bloodstream.  Clarify the docs.

Plus, it fixes an actual bug.  ICFRn, pfff.

Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
This commit is contained in:
Christoffer Dall 2014-06-14 22:34:04 +02:00
parent 9da48b5502
commit 7e362919a5
1 changed files with 7 additions and 6 deletions
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13
virt/kvm/arm/vgic.c
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@ -36,21 +36,22 @@
* How the whole thing works (courtesy of Christoffer Dall):
*
* - At any time, the dist->irq_pending_on_cpu is the oracle that knows if
* something is pending
* - VGIC pending interrupts are stored on the vgic.irq_pending vgic
* bitmap (this bitmap is updated by both user land ioctls and guest
* mmio ops, and other in-kernel peripherals such as the
* arch. timers) and indicate the 'wire' state.
* something is pending on the CPU interface.
* - Interrupts that are pending on the distributor are stored on the
* vgic.irq_pending vgic bitmap (this bitmap is updated by both user land
* ioctls and guest mmio ops, and other in-kernel peripherals such as the
* arch. timers).
* - Every time the bitmap changes, the irq_pending_on_cpu oracle is
* recalculated
* - To calculate the oracle, we need info for each cpu from
* compute_pending_for_cpu, which considers:
* - PPI: dist->irq_pending & dist->irq_enable
* - SPI: dist->irq_pending & dist->irq_enable & dist->irq_spi_target
* - irq_spi_target is a 'formatted' version of the GICD_ICFGR
* - irq_spi_target is a 'formatted' version of the GICD_ITARGETSRn
* registers, stored on each vcpu. We only keep one bit of
* information per interrupt, making sure that only one vcpu can
* accept the interrupt.
* - If any of the above state changes, we must recalculate the oracle.
* - The same is true when injecting an interrupt, except that we only
* consider a single interrupt at a time. The irq_spi_cpu array
* contains the target CPU for each SPI.