Re: [PATCH v6 07/11] xen/arm: implement FIXMAP_ADDR for MPU systems

[Julien Grall <julien@xxxxxxx>]

On 11/11/2022 07:56, Wei Chen wrote:
> Hi Julien,
>
> > -----Original Message-----
> > From: Julien Grall <julien@xxxxxxx>
> > Sent: 2022年11月10日 2:30
> > To: Wei Chen <Wei.Chen@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> > Cc: nd <nd@xxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>; Bertrand
> > Marquis <Bertrand.Marquis@xxxxxxx>; Volodymyr Babchuk
> > <Volodymyr_Babchuk@xxxxxxxx>
> > Subject: Re: [PATCH v6 07/11] xen/arm: implement FIXMAP_ADDR for MPU
> > systems
> >
> >
> >
> > On 09/11/2022 06:46, Wei Chen wrote:
> > > Hi Julien,
> > Hi Wei,
> >
> > > > -----Original Message-----
> > > > From: Julien Grall <julien@xxxxxxx>
> > > > Sent: 2022年11月7日 3:45
> > > > To: Wei Chen <Wei.Chen@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> > > > Cc: nd <nd@xxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> > Bertrand
> > > > Marquis <Bertrand.Marquis@xxxxxxx>; Volodymyr Babchuk
> > > > <Volodymyr_Babchuk@xxxxxxxx>
> > > > Subject: Re: [PATCH v6 07/11] xen/arm: implement FIXMAP_ADDR for MPU
> > > > systems
> > > >
> > > > Hi Wei,
> > > >
> > > > On 04/11/2022 10:07, Wei Chen wrote:
> > > > > FIXMAP is a special virtual address section for Xen to map some
> > > > > physical ram or device memory temporarily in initialization for
> > > > > MMU systems. FIXMAP_ADDR will return a virtual address by index
> > > > > for special purpose phys-to-virt mapping usage. For example,
> > > > > FIXMAP_ADDR(FIXMAP_CONSOLE) for early console mapping and
> > > > > FIXMAP_ADDR(FIXMAP_MISC) for copy_from_paddr.
> > > > To me, we are bending quite a bit the definition of the fixmap. There
> > > > are not many use of the FIXMAP within the code and I think it would
> > > > simply be better to abstract the use (or removing it when possible) and
> > > > avoid defining FIXMAP_ADDR() & co for MPU.
> > > I agree, if we don't mind to add some CONFIG_HAS_MPU in some generic
> > code.
> >
> > FAOD, this is not what I had in mind. Instead, it was to provide helper
> > which for !HAS_MPU would call fixmap and for HAS_MPU would do the work
> > to map the region in the MPU.
> Sorry, I am still confused about this comment, did you mean we can provider
> Some generic helpers like: early_map_console / eary_map_guest_memory.
> For non-MPU system, we still can call fixmap in these callers, but for
> MPU system, we have to map the region to MPU region?
Yes.

Cheers,

--
Julien Grall