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

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Message-ID: <4DD19D1F.3070506@linux.intel.com>
Date:	Mon, 16 May 2011 14:54:39 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	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>,
	"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.

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?

	-hpa

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