So I was chasing a bug today when I realized that some "drivers" in qemu do interesting things with memory regions. More specifically, cirrus emulation constantly flips the linear framebuffer between being mapped into the guest and being emulated MMIO (the latter for the purpose of image blits). This made me ponder ... whenever a memslot is "removed" like that (in the case for example where cirrus turns the fb into emulation), we need to ensure that any cached translation that involve those GPAs are flushed out of whatever caching (HW or SW) is done by the KVM arch code... So I started looking and the only thing I can find (let me know if I missed something) is kvm_arch_flush_shadow(). Is that it ? Because it doesn't take the memslot going away as an argument, so it doesn't know -what- to flush... Now I see that x86 just seems to flush everything, which is quite heavy handed considering how often cirrus does it, but maybe it doesn't have a choice (lack of reverse mapping from GPA ?). I also noticed that powerpc ... doesn't do anything :-) Ooops.... So all translations still present in the TLB will remain there, all translations present in the MMU hash table as well, etc... Now, in order to implement that properly and efficiently, we would need to at least get the GPA (if not the whole memslot). Do you have any objection (provided I didn't completely misunderstand something which is quite possible) to us adding that argument to kvm_arch_flush_shadow() ? We can easily put in a small patch adding that as an unused argument, and later get the proper implementation for powerpc. Another thing I noticed while at it is that my version of __kvm_set_memory_region() appears to call kvm_iommu_map_pages() whenever adding a memslot ... but never does the opposite unmapping when that memory slot is removed.... isn't that potentially an issue ? Cheers, Ben. -- 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
