Messages in this thread | | | Subject | Re: [RFC PATCH] virt_mmio: fix signature checking for BE guests | From | Benjamin Herrenschmidt <> | Date | Fri, 15 Feb 2013 11:07:56 +1100 |
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On Wed, 2013-02-13 at 15:28 +0000, Marc Zyngier wrote:
> 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.
It's actually a horrible idea :-)
What does "guest endianness" means from a qemu perspective if your emulated CPU can operate in either mode ?
It's actually been causing endless problems, besides linux doesn't have "Sane" MMIO accessors that say "current endianness". ioreadN/writeN are LE, realN/writeN are LE, ioreadNbe/iowriteNbe are BE always, the only "whatever my endianness is" are the __raw ones which also don't have barriers etc...
> > 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...
Cheers, Ben.
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