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Re: [PATCH 1/6] x86/vmx: Rewrite vmx_sync_pir_to_irr() to be more efficient
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 26 Jun 2024 15:16:15 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 26 Jun 2024 13:16:36 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 26.06.2024 15:04, Andrew Cooper wrote:
> One final thing.
>
> This logic here depends on interrupts not being enabled between these
> atomic actions, and entering non-root mode.
>
> Specifically, Xen must not service a pending delivery-notification
> vector between this point and the VMEntry microcode repeating the same
> scan on the PIR Descriptor.
>
> Getting this wrong means that we'll miss the delivery of vectors which
> arrive between here and the next time something causes a
> delivery-notification vector to be sent.
>
> However, I've got no idea how to reasonably express this with
> assertions. We could in principle have a per-cpu "mustn't enable
> interrupts" flag, checked in local_irq_enable/restore(), but it only
> works in HVM context, and gets too messy IMO.
I agree. It's also nothing this patch changes; it was like this before
already. If and when we can think of a good way of expressing it, then
surely we could improve things here.
Jan
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