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Re: [PATCH] x86/HVM: don't mark evtchn upcall vector as pending when vLAPIC is disabled
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 21 Nov 2022 12:14:50 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Paul Durrant <paul@xxxxxxx>
- Delivery-date: Mon, 21 Nov 2022 11:14:55 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21.11.2022 11:53, Roger Pau Monné wrote:
> On Mon, Nov 21, 2022 at 09:33:53AM +0100, Jan Beulich wrote:
>> On 18.11.2022 15:26, Roger Pau Monné wrote:
>>> Maybe best to add an ASSERT in vlapic_set_irq() to be sure the lapic is
>>> enabled, as other callers already check this before trying to inject?
>>
>> Perhaps, yes (once we've fixed paths where the check is presently
>> missing).
>
> Another option would be to unconditionally return 0 for IRR and ISR
> reads when the LAPIC is disabled, that would avoid having to force the
> event channel injection when the LAPIC is enabled, but there could be
> more than just the event channel vector queued in that way which would
> be against the spec.
Pre-existing set IRR bits remain set when moving into disabled mode. If
we faked zeros for reads, we'd violate the spec and undermine Linux'es
checking of the bits.
Jan
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