On Tue, Apr 12, 2016 at 08:39:02AM -0700, Jan Kiszka wrote: > On 2016-04-12 02:02, Peter Xu wrote:
[...] > > Yes, I should consider other x86 platforms like AMD. Thanks to point > > out. It seems that there are many places in the patchset that lacks > > thorough consideration about this. Will try to fix them in next > > version. > > > > Regarding to the above MSI solution: I'd say it is a good way to > > hide everything else behind. However, since we introduced one extra > > layer (MSI) which actually does not exist, not sure there would be > > problem too. Also, I feel it a little bit hacky if we "create" one > > MSI out of the air... For example, if someone tries to capture MSIs > > from QEMU inside in the APIC memory writes, he will see something he > > cannot explain if he never knows this hack's there. Considering the > > above, I would prefer hooks, or better to provide a callback (a > > function pointer that others like AMD can override) to do the > > translation. How do you think? > > The HPET does send MSIs, and I'm not sure how much different the > IOAPIC's message actually is. In any case, modelling it as MSI is > neither adding incorrectness nor making the code more complex (in fact, > the contrary is true!). Last but not least, it would be trivial to > filter out non-PCI MSI sources if we wanted to trace only PCI - because > we need to identify the origin anyway for remapping purposes. So, > explicit hooking looks like the wrong way to me. I am just not sure about the difference between IOAPIC's messages and MSI ones. For now, they seems very alike. However, I am not sure whether it would be not alike in the future. E.g., if one day, we extend APIC bus to support more than 255 CPUs (could it? I do not know for sure), here if we are with this "MSI layer", we would not be able to do that, since MSI only support 8 bits for destination ID field. That's my only worry now. If you (or Radim? or anyone more experienced on this than me) can confirm that this would never be a problem, I'd be glad to take the MSI way. Thanks. -- peterx
