linux-kernel - Re: Xen MMU's requirement to pin pages RO and initial_memory

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Message-ID: <alpine.DEB.2.00.1105171744230.12963@kaball-desktop>
Date:	Tue, 17 May 2011 18:51:58 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	"jeremy@...p.org" <jeremy@...p.org>,
	"hpa@...or.com" <hpa@...or.com>,
	Ian Campbell <Ian.Campbell@...citrix.com>,
	Keir Fraser <keir@....org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: Xen MMU's requirement to pin pages RO and
 initial_memory_mapping.

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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