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Re: [Xen-devel] irq_guest_eoi_timer interaction with MSI

  • To: Jan Beulich <jbeulich@xxxxxxxxxx>
  • From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
  • Date: Tue, 25 Nov 2008 08:30:40 +0000
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Tue, 25 Nov 2008 00:31:26 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AclO2Bk7V8jwjrrLEd2bbAAWy6hiGQ==
  • Thread-topic: [Xen-devel] irq_guest_eoi_timer interaction with MSI

On 25/11/08 08:15, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>> The fixmap stuff is a bit ugly and I would just have done a
>> map_domain_page_global() for 32-bit Xen (good enough as far as I'm
>> concerned). I'm not dead set against your approach if you like it very much,
>> though.
> But just as map_domain_page(), map_domain_page_global() can't be used
> out of IRQ context...

I would have kept the page mapped from when it was registered until domain
death. Same as we do for guest-registered vcpu_info.

>> Setting the need-a-hypercall bit looks racey. Don't you need to set the bit,
>> then check the guest didn't unmask meanwhile?
> We could, but I don't think it's strictly needed: The bit geting temporarily
> set (as opposed to the case where it's being set for the lifetime of the IRQ)
> is a performance optimization only anyway, i.e. to prevent the IRQ from
> remaining masked for longer than it really needs to be. But yes, I'll see
> whether the unmasking case can be taken care of without making the code
> much more complicated.

Yeah, okay.

 -- Keir

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