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Re: [cross-arch mess] [PATCH v2 1/2] x86/svm: Don't toggle local event delivery on stgi/clgi
- To: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 7 May 2026 12:28:20 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
- Delivery-date: Thu, 07 May 2026 11:28:34 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 07/05/2026 11:55 am, Ross Lagerwall wrote:
> There is no need to explicitly enable/disable local event delivery on
While the name of the function is local event, I think this needs to
state evtchn because "events" have a separate meaning in this area on x86.
Personally, I'd phrase it more sternly. The masking (or not) of evtchn
has nothing to do with GIF/IF.
> stgi/clgi since HVM event delivery already takes into account the state
STGI/CLGI.
> of the GIF (and IF). This ensures the behaviour is consistent regardless
> of whether vGIF is used.
>
> Fold the functions into the callers since they are now only a single
> assignment.
>
> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
For the patch itself, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
However there's another can of worms.
This patch deletes the only user of local_event_delivery_disable().
It does not delete the only user of local_event_delivery_enable() and
pulling that thread shows up a mess. The other caller is
vcpu_block_enable_events() which comes from SCHEDOP_block (probably
legitimate; enabling events is at least documented for this hypercall)
and hvm_hlt() which is definitely bogus.
It needs deleting, but we may want to instrument that path to see if we
ever clear the evtchn mask in practice, then run as many distros as we
can find.
Furthermore, while RISC-V and PPC have BUG() stubs for these functions,
ARM implements it as clearing regs->cpsr.irq_mask which is equally bogus
mixing virtualised evtchns with architectural interrupt handling.
That, equally, needs deleting but I'll have to defer to the ARM
maintainers (CC'd) on how to do it safely.
~Andrew
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