Re: [Xen-devel] [PATCH 1/5] Add MSI support to XEN

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 28/3/08 09:49, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

>> Yes, the synchronisation is pretty easy though. We just have
>> to add a layer
>> of emulation to PV guest accesses to 0xcf8/0xcfc.
> 
> Yes, a small tricky however is, the owner vcpu may be scheduled
> out between 0xcf8 and 0xcfc access, when another pcpu is trying
> to access PCI config space like masking MSI within do_IRQ...
> Maybe Xen need to emulate 0xcf8/0xcfc pair without return to
> guest in the middle. :-)

Not at all. You track the guest's 0xcf8 value in the vcpu structure, and
issue the physical 0xcf8/0xcfc access as a pair, under a spinlock, whenever
the guest writes 0xcfc.

 -- Keir



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