On 13/02/13 15:08, Pawel Moll wrote: > On Wed, 2013-02-13 at 14:25 +0000, Marc Zyngier wrote: >> Using readl() to read the magic value and then memcmp() to check it >> fails on BE, as bytes will be the other way around (by virtue of >> the registers to follow the endianess of the guest). > > Hm. Interesting. I missed the fact that readl() as a "PCI operation" > will always assume LE values... > >> Fix it by encoding the magic as an integer instead of a string. >> So I'm not completely sure this is the right fix, > > It seems right, however... > >> - Using __raw_readl() instead. Is that a generic enough API? >> > ... this implies that either the spec is wrong (as it should say: the > device registers are always LE, in the PCI spirit) or all readl()s & co. > should be replaced with __raw equivalents. Well, the spec clearly says that the registers reflect the endianess of the guest, and it makes sense: when performing the MMIO access, KVM needs to convert between host and guest endianess. > Having said that, does the change make everything else work with a BE > guest? (I assume we're talking about the guest being BE, right? ;-) If > so it means that the host is not following the current spec and it > treats all the registers as LE. Yes, I only care about a BE guest. And no, not much is actually working (kvmtool is not happy about the guest addresses it finds in the virtio-ring). Need to dive into it and understand what needs to be fixed... >> - Reading the MAGIC register byte by byte. Is that allowed? The spec >> only says it is 32bit wide. > > And the spirit of the spec was: _exactly 32bit wide_. It's just simpler > to implement one access width on the host side. I guessed as much... M. -- Jazz is not dead. It just smells funny... _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
