Re: [Xen-devel] [PATCH v2 22/55] x86_64/mm: switch to new APIs in paging_init

[Hongyan Xia <hongyax@xxxxxxxxxx>]

On 01/10/2019 12:51, Wei Liu wrote:
> On Mon, Sep 30, 2019 at 11:33:14AM +0100, Hongyan Xia wrote:
> > From: Wei Liu <wei.liu2@xxxxxxxxxx>
> >
> > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > Signed-off-by: Hongyan Xia <hongyax@xxxxxxxxxx>
> >
> > ---
> > Changed since v1:
> >    * use a global mapping for compat_idle_pg_table_l2, otherwise
> >      l2_ro_mpt will unmap it.
> Hmmm... I wonder why XTF didn't catch this.
Well, probably because this only shows up when we actually remove all fast 
paths and the direct map. If we just apply this batch, unmap on the direct map 
is just a no-op. I caught this with my later patches.
> If we really want to go all the way to eliminate persistent mappings
> for page tables, the code should be changed such that:
>
> 1. compat_idle_pg_table_l2 should be changed to store mfn, not va.
> 2. map and unmap that mfn when access to the compat page table is
>     required.
Sounds sensible and more consistent with other PTEs.

Hongyan

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