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Date: Tue, 14 Jun 2011 15:26:01 -0500
From: Scott Wood <scottwood@freescale.com>
To: Thomas De Schampheleire <patrickdepinguin+linuxppc@gmail.com>
Subject: Re: Mapping an executable page
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On Tue, 14 Jun 2011 10:56:31 +0200
Thomas De Schampheleire <patrickdepinguin+linuxppc@gmail.com> wrote:

> * Therefore, to make sure that the mapping I intended with __ioremap()
> is actually reflected in the TLB tables, I added dummy reads of each
> page in the TLB, prior to jumping to the boot code, as follows:
>                 /* make sure memory is read, once every 4Kbyte is enough */
>                 for (p = vaddr; p < vaddr + map_size; p += 0x1000) {
>                         unsigned long dummy = *(volatile unsigned long *)p;
>                         (void)dummy;
>                 }
> 
> * After these changes (make sure all code is mapped + make sure to
> read all pages so that the TLBs are updated), my scenario works fine.

This is fragile -- you are assuming that it's possible to fit this
set of pages in TLB0 all at once, and that none of them will be
evicted/invalidated by the time you're done.

If you really need to do this, I sugest using settlbcam() from
arch/powerpc/mm/fsl_booke_mmu.c to create TLB1 entries with IPROT set.

Better still if you could live with whatever memory the kernel has already
pinned.

-Scott