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[Xen-devel] Re: [PATCH 2/4] x86,xen: introduce x86_init.mapping.pagetabl

To: Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 2/4] x86,xen: introduce x86_init.mapping.pagetable_reserve
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Mon, 18 Apr 2011 15:09:21 +0100
Cc: "jeremy@xxxxxxxx" <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "konrad.wilk@xxxxxxxxxx" <konrad.wilk@xxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, "mingo@xxxxxxx" <mingo@xxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxxxxxxxx>, "yinghai@xxxxxxxxxx" <yinghai@xxxxxxxxxx>
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On Thu, 14 Apr 2011, Stefano Stabellini wrote:
> On Thu, 14 Apr 2011, H. Peter Anvin wrote:
> > On 04/14/2011 04:30 AM, Stefano Stabellini wrote:
> > > 
> > > I hope that the other email I have just sent clarifies the purpose of
> > > the hook.
> > >           
> > 
> > You're commingling rationale and (proposed) semantics.  BOTH need to be
> > stated clearly.
> Sorry I didn't answer the right question straight away.
> The semantics follow:
> It is as if there is an implicit pvop after find_early_table_space
> that exports the range pgt_buf_start - pgt_buf_top.
> The range indicated is used, and it is the only range used, for the initial
> kernel pagetable pages.
> The range indicated is an overestimate.
> It is implicit because we use the pgt_buf_* variables directly but
> nonetheless it was in the first version of the patch.
> After the pagetable setup done by kernel_physical_mapping_init, we know
> exactly how many pages we actually used for the initial kernel
> pagetables and how many are left unused.
> The purpose of the second pvop (x86_init.mapping.pagetable_reserve) is
> to notify sub-architectures of the actual range used for initial kernel
> pagetable pages and partially revoke the previous indication.
> If you agree with the proposed semantics above, I'll add the description
> to the commit message as well as the code. I could also modify the
> syntax of the new pvop call to better suit the semantics and/or restore
> the first pvop call.


Sorry, I don't mean to be pushy, it is just that I'll be AFK for 12 days
starting from next Friday and I think that this issue should really be
fixed in time for the 2.6.39 release, otherwise no 2.6.39 kernels will
be able to boot on any xen system.

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