Re: [Xen-devel] [PATCH 15/17] xen/arm64: head: Rework and document setup_fixmap()

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 26/06/2019 20:30, Julien Grall wrote:
> On 6/26/19 8:01 PM, Stefano Stabellini wrote:
> > On Mon, 10 Jun 2019, Julien Grall wrote:
> > > At the moment, the fixmap table is only hooked when earlyprintk is used.
> > > This is fine today because in C land, the fixmap is not used by anyone
> > > until the the boot CPU is switching to the runtime page-tables.
> > >
> > > In the future, the boot CPU will not switch between page-tables to avoid
> > > TLB conflict. This means the fixmap table will need to be hooked before
> > > any use. For simplicity, setup_fixmap() will now do that job.
> > Can I ask you to reword this slightly, especially the last sentence? It
> > took me a while to understand what you meant. I suggest:
> >
> >   In the future, the boot CPU will not switch between page-tables to
> >   avoid any TLB conflicts. Thus, the fixmap table will need to be always
> >   hooked before any use. Let's start doing it now in setup_fixmap().
> I will update the commit message.
I realized the commit message I wrote is inaccurate and reflected to your 
rewording.

Not all the platforms will generate a TLB conflict abort. Some of them may just 
decide to use an amalgamation of two entries (see "TLB matching" page D5-2500 in 
ARM DDI 0487D.b).
I will replace "any TLB conflicts" by "TLB incoherency".

> > Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx> >
Let me know if you are happy with the change suggested.

Cheers,

--
Julien Grall

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