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xen-devel
RE: [Xen-devel] VT/ioemu: vga memory access?
> -----Original Message-----
> From: Gerd Hoffmann [mailto:kraxel@xxxxxxx]
> Sent: 16 May 2006 16:57
> To: Petersson, Mats
> Cc: Xen devel list
> Subject: Re: [Xen-devel] VT/ioemu: vga memory access?
>
> Hi,
>
> >> How is vga vram access handled in the device model? Is there some
> >> kind of notification system, by mapping those pages
> read-only, then
> >> trap and forward any write access to qemu-dm?
> >
> > Actually, xen HVM handles all memory mapped IO in the same
> way - pages
> > are not present, causing a page-fault and then checking the address
> > against a "memory mapped IO range" in the function
> > mmio_space() [I haven't looked inside this function], and if it's a
> > match it's passed to QEMU via handle_mmio().
>
> I think I found the bug. It's actually in handle_mmio() ;)
> The "case INSTR_MOVS" has code which deals with page
> boundaries. The code allways _adds_ the count (ecx) to
> figure whenever the "repz movsb" crosses a page boundary or
> not. In case the direction flag is set this isn't correct,
> it should subtract instead. Subsequently it mis-calculates
> count, making it _larger_ than it was because the copy
> wouldn't have crossed a page boundary, leading to the
> negative ecx value in the register dump ...
I think you're right...
I'll write some simple test code to check it out, and let you know...
--
Mats
>
> cheers,
>
> Gerd
>
> --
> Gerd Hoffmann <kraxel@xxxxxxx>
> Erst mal heiraten, ein, zwei Kinder, und wenn alles läuft
> geh' ich nach drei Jahren mit der Familie an die Börse.
> http://www.suse.de/~kraxel/julika-dora.jpeg
>
>
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