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Re: [PATCH v2 4/4] x86/dpci: remove the dpci EOI timer
- To: <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Fri, 15 Jan 2021 15:56:00 +0100
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On Fri, Jan 15, 2021 at 03:28:20PM +0100, Roger Pau Monne wrote:
> Current interrupt pass though code will setup a timer for each
> interrupt injected to the guest that requires an EOI from the guest.
> Such timer would perform two actions if the guest doesn't EOI the
> interrupt before a given period of time. The first one is deasserting
> the virtual line, the second is perform an EOI of the physical
> interrupt source if it requires such.
>
> The deasserting of the guest virtual line is wrong, since it messes
> with the interrupt status of the guest. This seems to have been done
> in order to compensate for missing deasserts when certain interrupt
> controller actions are performed. The original motivation of the
> introduction of the timer was to fix issues when a GSI was shared
> between different guests. We believe that other changes in the
> interrupt handling code (ie: proper propagation of EOI related actions
> to dpci) will have fixed such errors now.
>
> Performing an EOI of the physical interrupt source is redundant, since
> there's already a timer that takes care of this for all interrupts,
> not just the HVM dpci ones, see irq_guest_action_t struct eoi_timer
> field.
>
> Since both of the actions performed by the dpci timer are not
> required, remove it altogether.
>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Changes since v1:
> - Add parentheses.
This is a lie because I forgot to refresh the patch before sending.
Will send a new version if required.
Thanks, Roger.
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