Re: [PATCH] ARM: decompressor: Flush tlb before swiching domain 0to client mode

[Santosh Shilimkar]

On Wednesday 12 December 2012 11:27 PM, Arve Hjønnevåg wrote:
> On Wed, Dec 12, 2012 at 2:10 AM, Santosh Shilimkar
> <santosh.shilimkar@xxxxxx> wrote:
> > On Wednesday 12 December 2012 02:41 AM, Arve Hjønnevåg wrote:
> > > If the bootloader used a page table that is incompatible with domain 0
> > > in client mode, then swithing domain 0 to client mode causes a fault
> > > if we don't flush the tlb after updating the page table pointer.
> > >
> > > Signed-off-by: Arve Hjønnevåg <arve@xxxxxxxxxxx>
> > > ---
> > >    arch/arm/boot/compressed/head.S |    1 +
> > >    1 files changed, 1 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/arch/arm/boot/compressed/head.S
> > > b/arch/arm/boot/compressed/head.S
> > > index 90275f0..9c8034c 100644
> > > --- a/arch/arm/boot/compressed/head.S
> > > +++ b/arch/arm/boot/compressed/head.S
> > > @@ -704,6 +704,7 @@ __armv7_mmu_cache_on:
> > >                  bic     r6, r6, #1 << 31        @ 32-bit translation
> > > system
> > >                  bic     r6, r6, #3 << 0         @ use only ttbr0
> > >                  mcrne   p15, 0, r3, c2, c0, 0   @ load page table pointer
> > > +               mcrne   p15, 0, r0, c8, c7, 0   @ flush I,D TLBs
> > >                  mcrne   p15, 0, r1, c3, c0, 0   @ load domain access
> > > control
> > >                  mcrne   p15, 0, r6, c2, c0, 2   @ load ttb control
> > >    #endif
> > The TLB's are already flushed few lines above so above patching
> > shouldn't help if it was really dirty TLB entry issue. I suspect that
> > your boot-loader clean-up [1] function may not be taking care of
> > flushing caches which could potetially lead to the issue.
> >
> > Have you checked that ?
>
> No, the problem is that the mmu is on when that first tlb flush
> happens so the tlb entry for the code that is executing gets reloaded
> from the old page table. This is probably a bootloader bug, but I
> don't have the bootloader source and 3.4 boots with the same
> bootloader.
Yes. The MMU is suppose to be turned off by boot-loader before jumping
to the kernel. That explains the problem. No need to patch
the kernel here.

Regards
Santosh
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/