Re: [PATCH v5 02/14] ARM: Section based HYP idmap

Gleb Natapov
2013-01-14T11:08:14Z

On Mon, Jan 14, 2013 at 10:49:53AM +0000, Will Deacon wrote:
> On Mon, Jan 14, 2013 at 10:27:21AM +0000, Gleb Natapov wrote:
> > On Tue, Jan 08, 2013 at 01:38:48PM -0500, Christoffer Dall wrote:
> > > Add a method (hyp_idmap_setup) to populate a hyp pgd with an
> > > identity mapping of the code contained in the .hyp.idmap.text
> > > section.
> > >
> > > Offer a method to drop this identity mapping through
> > > hyp_idmap_teardown.
> > >
> > > Make all the above depend on CONFIG_ARM_VIRT_EXT and CONFIG_ARM_LPAE.
> > >
> > > Cc: Will Deacon <will.deacon@arm.com>
> > > Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
> > > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> > > Signed-off-by: Christoffer Dall <c.dall@virtualopensystems.com>
> > > ---
> > > arch/arm/include/asm/idmap.h | 1 +
> > > arch/arm/include/asm/pgtable-3level-hwdef.h | 1 +
> > > arch/arm/kernel/vmlinux.lds.S | 6 +++
> > > arch/arm/mm/idmap.c | 54 ++++++++++++++++++++++-----
> > > 4 files changed, 50 insertions(+), 12 deletions(-)
>
> [...]
>
> > > -static void identity_mapping_add(pgd_t *pgd, unsigned long addr, unsigned long end)
> > > +static void identity_mapping_add(pgd_t *pgd, const char *text_start,
> > > + const char *text_end, unsigned long prot)
> > > {
> > > - unsigned long prot, next;
> > > + unsigned long addr, end;
> > > + unsigned long next;
> > > +
> > > + addr = virt_to_phys(text_start);
> > > + end = virt_to_phys(text_end);
> > How does this work with phys addresses greater than 32bit (with
> > LPAE)? This was the same before the patch too, but I am still
> > curious. Since __virt_to_phys() returns unsigned long kernel cannot be
> > put in high memory, right?
>
> Well, AArch32 (arch/arm/) only supports 32-bit virtual addresses by virtue
> of the fact that our registers are only 32 bits wide, so we can't
> identity-map physical addresses above the 4GB boundary.
>
Ah, of course. This is ident map so by definition it cannot map phys
addresses above 4G. And since __virt_to_phys() suppose to work only on
ident map it's OK to returns unsigned long.

> You may want to look at the keystone patches from TI for insight about
> kernels at high (>32-bit) addresses, although I've not seen any activity
> around that for some time now (which is a pity, because the code-patching
> stuff was in a good shape).
>
> Will

--
Gleb.