Hi Uwe,
On 04/06/14 00:11, Uwe Kleine-König wrote:
On Tue, Jun 03, 2014 at 10:14:55PM +1000, Greg Ungerer wrote:
I think it would be OK to define TASK_SIZE to 0xffffffff for !MMU.
blackfin, frv and m68k also do this. c6x does define it to 0xFFFFF000 to
leave space for error codes.
I did that same change for m68k in commit cc24c40 ("m68knommu: remove
size limit on non-MMU TASK_SIZE"). For similar reasons as you need to
now.
ok.
Thoughts?
The problem is that current linus/master (and also next) doesn't boot on
my ARM-nommu machine because the user string functions (strnlen_user,
strncpy_from_user et al.) refuse to work on strings above TASK_SIZE
which in my case also includes the XIP kernel image.
I seem to recall that we were not considering flash or anything else
other than RAM when defining that original TASK_SIZE (back many, many
years ago). Some of the address checks you list above made some sense
if you had everything in RAM (though only upper bounds are checked).
The thinking was some checking is better than none I suppose.
What is the actual meaning of TASK_SIZE? The maximal value of a valid
userspace address?
Yes (as Geert pointed out :-)
The limit of virtual userspace addresses.
Setting a hard coded memory size in CONFIG_DRAM_SIZE is not all that
fantastic either...
Not sure what you mean? Having CONFIG_DRAM_SIZE at all or use it for
boundary checking?
Having the DRAM size be a configure time constant. And as you have
found RAM isn't the only place in the physical address space that
code will necessarily access.
CONFIG_DRAM_SIZE is hardly used apart from defining TASK_SIZE:
- #define END_MEM (UL(CONFIG_DRAM_BASE) + CONFIG_DRAM_SIZE)
which is only used to define MODULES_END. Ap
- Some memory configuration using cp15 registers in
arch/arm/mm/proc-arm{740,940,946}.S
For the former I'd say better use 0xffffffff, too. For the latter I
wonder if we should just drop CPU_ARM740T, CPU_ARM940T and CPU_ARM946E.
These are only selectable if ARCH_INTEGRATOR and are not selected by
other symbols. As ARCH_INTEGRATOR selects ARM_PATCH_PHYS_VIRT since
commit fe9891454473 (ARM: integrator: Default enable
ARM_PATCH_PHYS_VIRT, AUTO_ZRELADDR) for Linux 3.13 and
ARM_PATCH_PHYS_VIRT depends on MMU the Integrator-noMMU targets are
broken anyhow.
I will prepare a patch series with some cleanups.
I have no idea how many people would be using those older ARM CPU types.
It was hard to get much interest for them in mainline even years ago.
Regards
Greg
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