Re: [Xen-devel] [PATCH v7 21/28] xen/arm: ITS: Add GICR register emulation

[Vijay Kilari <vijay.kilari@xxxxxxxxx>]

On Mon, Sep 28, 2015 at 3:23 PM, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
> On Sat, 2015-09-26 at 21:38 +0530, Vijay Kilari wrote:
>
>>  LPI property table is accessed in interrupt context. So interrupts
>> are disabled.
>
> Interrupts a reenabled while handling an interrupt, so a higher priority
> interrupt can still interrupt things.
>
> See the use of local_irq_enable in gic_interrupt.

true, for this reason, I have taken spin lock with disabled
interrrupts when reading guest LPI table.

Question is to avoid disabling interrupts for a  long time for about 8K/16K lpis
state update.

The LPI state update from guest LPI property table is done when guest
updates GICR_CTLR.EnableLPIs to 1.
(I am doing this in next revision).

So we can make a check for guest's GICR_CTLR.EnableLPIs field before
injecting LPIs to the domain. As per design
GICR_CTLR.EnableLPIs should be 0 when updating guest property table.
i.e updating GICR_PROPBASER.
So that we don't need to disable interrupts(LPIs are already disabled)
while reading guest LPI table.

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