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[Xen-devel] Re: Xen MMU's requirement to pin pages RO and initial_memory

To: "H. Peter Anvin" <hpa@xxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: Xen MMU's requirement to pin pages RO and initial_memory_mapping.
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Tue, 17 May 2011 18:51:58 +0100
Cc: "jeremy@xxxxxxxx" <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir@xxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, "hpa@xxxxxxxxx" <hpa@xxxxxxxxx>, "yinghai@xxxxxxxxxx" <yinghai@xxxxxxxxxx>
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CC'ing Keir in case he knows something I am missing.

On Mon, 16 May 2011, H. Peter Anvin wrote:
> On 05/16/2011 08:41 AM, Konrad Rzeszutek Wilk wrote:
> >> They become pagetable pages when:
> >>
> >> - they are explicitly pinned by pin_pagetable_pfn
> >>
> >> - they are hooked into the current pagetable
> > 
> > Ok, so could we use those two calls to trigger the pagetable walk
> > and mark them RO as appropiate? Which call sites are those? The
> > xen_set_pgd/xen_set_pud/xen_set_pmd ? Presumarily we don't have
> > to do that for the PTE's that are already mapped (as
> > xen_setup_kernel_pagetable, and xen_map_identity_early do this
> > already).
> > 
> >> Like you wrote, considering that the x86_64 version of
> >> kernel_physical_mapping_init hooks the pagetable pages into the
> >> currently used pagetable, it wouldn't be possible to mark the pagetable
> >> pages RO after init_memory_mapping.
> > 
> Doesn't Xen have some kind of compatibility mode which could be used
> during setup?
Unfortunately not that I am aware.

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