[Xen-devel] Re: [PATCH 6/8] xen/debug: WARN_ON when 1-1 but no _PAGE_IOMAP flag set.

[Keir Fraser <keir@xxxxxxx>]

On 06/01/2011 21:59, "Konrad Rzeszutek Wilk" <konrad.wilk@xxxxxxxxxx> wrote:

>> Always 0x55...55 (for m2p entries that exist), else page fault on access to
>> the non-existent m2p entry (m2p entries only guaranteed to exist for ram).
>> Perhaps the 0xff...ff values come from Linux's own fixup code handling a
>> faulting read access of the m2p array? If so you could return 0x55...55
>> instead and avoid checking for 0xff...ff. I really don't know how you could
>> get 0xff...ff for non-RAM pages from Xen itself.
> 
> The non-RAM pages are assinged to a DOMID_IO (arch_init_memory), for example:
> 
>  298     /* First 1MB of RAM is historically marked as I/O. */
>  299     for ( i = 0; i < 0x100; i++ )
>  300         share_xen_page_with_guest(mfn_to_page(i), dom_io,
> XENSHARE_writable);
> 
> and share_xen_page.. sets that page to INVALID_M2P_ENTRY.
> 
> But I could also be reading the code wrongly?

You're right, I missed that.

 -- Keir



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