Re: [PATCH v3 2/2] ARM : change fixmap mapping region to support 32 CPUs

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Wed, Aug 06, 2014 at 10:28:37AM -0700, Kees Cook wrote:
> That's what I was thinking. I tried this, and things are still weird,
> though I think I'm narrowing it down. I made the early_pte_alloc
> happen, but after boot it doesn't show up in
> /sys/kernel/debug/kernel_page_tables. When I attempt a fixmap text
> poke, I get this out of dmesg (lkdtm is reporting the address returned
> from the patch mapping):
> 
> lkdtm: 80421ac0 mapped RW via ffdefac0
> Unable to handle kernel paging request at virtual address ffdefac0
> pgd = 9e888000
> [ffdefac0] *pgd=9fffc811, *pte=00000000, *ppte=00000000
> Internal error: Oops: 807 [#1] SMP ARM
> 
> The target address (0xffdefac0) is correct; it's in the range set aside:
> 
> #define FIXADDR_START           0xffc00000UL
> #define FIXADDR_END             0xffe00000UL
> #define FIXADDR_TOP             (FIXADDR_END - PAGE_SIZE)
> 
> enum fixed_addresses {
>         /* Support 16 CPUs for kmap as the first region of fixmap entries. */
>         FIX_KMAP_BEGIN,
>         FIX_KMAP_END = 15,
> 
>         /* Support writing RO kernel text via kprobes, jump labels, etc. */
>         FIX_TEXT_POKE0,
>         FIX_TEXT_POKE1,
> 
>         __end_of_fixed_addresses
> };
> 
> But the resulting PTE is in totally the wrong location as reported by
> /sys/kernel/debug/kernel_page_tables:
> 
> ---[ Fixmap Area ]---
> 0xfffef000-0xffff0000           4K     RW NX SHD MEM/CACHED/WBWA
> 
> I continue to dig...

This sounds like you have an erroneous merge conflict resolution.  You
seem to be poking into TOP_PTE rather than fixmap_page_table.

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