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xen-devel
[Xen-devel] Re: one question to p2m table entry type
At 09:17 +0100 on 05 May (1273051073), Jiang, Yunhong wrote:
> Tim/Keir, I noticed that when translatiing p2m table type and p2m pte entry
> flags, there are difference handling for x86_64 and x32 like:
>
> in p2m_type_to_flags:
> #ifdef __x86_64__
> flags = (unsigned long)(t & 0x3fff) << 9;
> #else
> flags = (t & 0x7UL) << 9;
> #endif
>
> in p2m_flags_to_type:
> /* Type is stored in the "available" bits */
> #ifdef __x86_64__
> return (flags >> 9) & 0x3fff;
> #else
> return (flags >> 9) & 0x7;
>
> But since we don't support pure 32 bit xen hypervisor any more, and
> for 32 PAE, we are sure have enough bit to keep these flags, why do we
> need these special handling? Are there any special reason for it?
The Intel SDMs (section 3.8.5, figure 3-20 in the copy in front of me)
only define three available bits in PAE PTEs; all bits above MAXPHYADDR
are reserved. If we can rely on the manuals being wrong about that, we
can extend the number of p2m types on 32-bit XEN. :)
Cheers,
Tim.
--
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, XenServer Engineering
Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)
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