linux-kernel - Re: [PATCH 26/46] x86, mm, Xen: Remove mapping_pagetable

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Date:	Wed, 14 Nov 2012 11:19:06 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Jacob Shin <jacob.shin@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 26/46] x86, mm, Xen: Remove mapping_pagetable_reserve()

On Tue, 13 Nov 2012, Yinghai Lu wrote:
> On Tue, Nov 13, 2012 at 8:36 AM, Stefano Stabellini
> <stefano.stabellini@...citrix.com> wrote:
> > On Mon, 12 Nov 2012, Yinghai Lu wrote:
> >> Page table area are pre-mapped now after
> >>       x86, mm: setup page table in top-down
> >>       x86, mm: Remove early_memremap workaround for page table accessing on 64bit
> >>
> >> mapping_pagetable_reserve is not used anymore, so remove it.
> >
> > You should mention in the description of the patch that you are
> > removing mask_rw_pte too.
> >
> > The reason why you can do that safely is that you previously modified
> > allow_low_page to always return pages that are already mapped, moreover
> > xen_alloc_pte_init, xen_alloc_pmd_init, etc, will mark the page RO
> > before hooking it into the pagetable automatically.
> 
> updated change log:
> ---
> x86, mm, Xen: Remove mapping_pagetable_reserve()
> 
> Page table area are pre-mapped now after
>         x86, mm: setup page table in top-down
>         x86, mm: Remove early_memremap workaround for page table
> accessing on 64bit
> 
> mapping_pagetable_reserve is not used anymore, so remove it.
> 
> Also remove operation in mask_rw_pte(), as modified allow_low_page
> always return pages that are already mapped, moreover
> xen_alloc_pte_init, xen_alloc_pmd_init, etc, will mark the page RO
> before hooking it into the pagetable automatically.
> 
> -v2: add changelog about mask_rw_pte() from Stefano.

Thanks

 
> >
> > [ ... ]
> >
> > you should just get rid of mask_rw_pte completely
> 
> then how about 32bit mask_rw_pte? Maybe you can clean up that later?

Yes, I can clean it up later.

However it is trivial: mask_rw_pte is only called by xen_set_pte_init
and in the 32bit case it already returns pte without modifications.

I would just remove the call to mask_rw_pte in xen_set_pte_init.
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