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xen-devel
[Xen-devel] Re: [PATCH 6/8] xen/debug: WARN_ON when 1-1 but no _PAGE_IOM
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To: |
Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH 6/8] xen/debug: WARN_ON when 1-1 but no _PAGE_IOMAP flag set. |
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From: |
Keir Fraser <keir@xxxxxxx> |
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Date: |
Thu, 06 Jan 2011 22:17:06 +0000 |
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Cc: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>, "hpa@xxxxxxxxx" <hpa@xxxxxxxxx> |
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Thu, 06 Jan 2011 14:18:47 -0800 |
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[PATCH 6/8] xen/debug: WARN_ON when 1-1 but no _PAGE_IOMAP flag set. |
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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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