On Wed, Feb 13, 2013 at 03:28:52PM +0000, Marc Zyngier wrote: > 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... Does it work for qemu? I know people were using virtio on BE there. > >> - 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
