Re: [PATCH] Re: [Xen-devel] [PATCH] Std VGA Performance

To:	Alex Williamson <alex.williamson@xxxxxx>
Subject:	Re: [PATCH] Re: [Xen-devel] [PATCH] Std VGA Performance
From:	Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date:	Tue, 30 Oct 2007 16:24:47 +0000
Cc:	xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Robert Phillips <rphillips@xxxxxxxxxxxxxxx>, Ben Guthro <bguthro@xxxxxxxxxxxxxxx>, xen-ia64-devel <xen-ia64-devel@xxxxxxxxxxxxxxxxxxx>
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Yeah, hopefully that's a bug in the comment. I would expect 4-byte accesses
to be possible and be handled. As for 8-byte accesses, they can certainly
happen, why not? Unlikely at start of day, but once we're in x86/64 mode
there's no reason why not.

 -- Keir

On 30/10/07 16:19, "Alex Williamson" <alex.williamson@xxxxxx> wrote:

>    Yes, you're right, but easy to overlook, and I'm not sure how it
> works on x86.  I copied the x86 code for filling in the buffered ioreq,
> but failed to notice that it attempts to store 4 bytes of data into a 2
> byte field...  The comment for the size entry in buf_ioreq could be
> interpreted that only 1, 2, and 8 bytes are expected, but I definitely
> see 4 bytes on occasion.  I'd guess x86 has a bug here that's simply not
> exposed because of the 16bit code that's probably being used to
> initialize VGA.  I also question the 8 byte support, which is why I
> skipped it in the patch below.  Wouldn't an 8 byte MMIO access that
> isn't a timeoffset be possible?  Keir, please apply this to the staging
> tree.  Thanks,



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