On Thursday 07 May 2009, Gregory Haskins wrote: > Arnd Bergmann wrote: > > An mmio that goes through a PF is a bug, it's certainly broken on > > a number of platforms, so performance should not be an issue there. > > > > This may be my own ignorance, but I thought a VMEXIT of type "PF" was > how MMIO worked in VT/SVM. You are right that all MMIOs (and PIO on most non-x86 architectures) are handled this way in the end. What I meant was that an MMIO that traps because of a simple pointer dereference as in __raw_writel is a bug, while any actual writel() call could be diverted to do an hcall and therefore not cause a PF once the infrastructure is there. > I guess the problem that was later pointed out is that we cannot discern > which devices might be pass-through and therefore should not be > revectored through a HC. But I am even less knowledgeable about how > pass-through works than I am about the MMIO traps, so I might be > completely off here. An easy way to deal with the pass-through case might be to actually use __raw_writel there. In guest-to-guest communication, the two sides are known to have the same endianess (I assume) and you can still add the appropriate smp_mb() and such into the code. Arnd <>< -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
