On 1/28/19 5:43 AM, Paul Mackerras wrote: > On Thu, Jan 24, 2019 at 08:25:15AM +1100, Benjamin Herrenschmidt wrote: >> On Wed, 2019-01-23 at 21:30 +1100, Paul Mackerras wrote: >>>> Afaik bcs we change the mapping to point to the real HW irq ESB page >>>> instead of the "IPI" that was there at VM init time. >>> >>> So that makes it sound like there is a whole lot going on that hasn't >>> even been hinted at in the patch descriptions... It sounds like we >>> need a good description of how all this works and fits together >>> somewhere under Documentation/. >>> >>> In any case we need much more informative patch descriptions. I >>> realize that it's all currently in Cedric's head, but I bet that in >>> two or three years' time when we come to try to debug something, it >>> won't be in anyone's head... >> >> The main problem is understanding XIVE itself. It's not realistic to >> ask Cedric to write a proper documentation for XIVE as part of the >> patch series, but sadly IBM doesn't have a good one to provide either. > > There are: (a) the XIVE hardware, (b) the definition of the XIVE > hypercalls that guests use, and (c) the design decisions around how to > implement that hypercall interface. We need to get (b) published > somehow, but it is mostly (c) that I would expect the patch > descriptions to explain. > > It sounds like there will be a mapping to userspace where the pages > can sometimes point to an IPI page and sometimes point to a real HW > irq ESB page. Just to be clear. In both cases, these pages are real HW ESB pages. They are just attached to a different controller : the XIVE IC for the IPIs and the PHB4 for the others. > That is, the same guest "hardware" irq number sometimes > refers to a software-generated interrupt (what you called an "IPI" > above) and sometimes to a hardware-generated interrupt. That fact,> the reason why it is so and the consequences all need to be explained > somewhere. They are really not obvious and I don't believe they are > part of either the XIVE hardware spec or the XIVE hypercall spec. I tried to put the reasons behind the current approach in another thread, not saying this is the correct one. Thanks, C.
