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    SubjectRe: [RFC PATCH] virt_mmio: fix signature checking for BE guests
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    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.

    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.

    > - 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.

    Paweł


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