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Re: [Xen-devel] [PATCH 2/2] x86: add pte_set_flags/clear_flags forptef

To: Jan Beulich <jbeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 2/2] x86: add pte_set_flags/clear_flags forpteflag manipulation
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Mon, 26 Jan 2009 11:54:11 -0800
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>
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Jan Beulich wrote:
Whether a pte is live doesn't matter here: If you change P on Xen, the
frame number representation *must* change from/to PFN to/from MFN.
In no case (other than iomem pages) is it allowed to flip just this bit.

Yes, true. Same with _PAGE_SPECIAL, which is actually flipped by code here. I guess a warning here might be useful, but really the calling code needs to be properly disciplined; after all setting P on a swap entry is no fun either.

   J

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