Le 14/04/2021 à 07:59, Anshuman Khandual a écrit :

On 4/14/21 10:52 AM, Christophe Leroy wrote:

quoted

Le 14/04/2021 à 04:54, Anshuman Khandual a écrit :

quoted

Currently most platforms define FIRST_USER_ADDRESS as 0UL duplicating the
same code all over. Instead define a new option ARCH_HAS_FIRST_USER_ADDRESS
for those platforms which would override generic default FIRST_USER_ADDRESS
value 0UL. This makes it much cleaner with reduced code.

Cc: linux-alpha@vger.kernel.org
Cc: linux-snps-arc@lists.infradead.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-csky@vger.kernel.org
Cc: linux-hexagon@vger.kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-mips@vger.kernel.org
Cc: openrisc@lists.librecores.org
Cc: linux-parisc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-riscv@lists.infradead.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: sparclinux@vger.kernel.org
Cc: linux-um@lists.infradead.org
Cc: linux-xtensa@linux-xtensa.org
Cc: x86@kernel.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <redacted>
---
   arch/alpha/include/asm/pgtable.h             | 1 -
   arch/arc/include/asm/pgtable.h               | 6 ------
   arch/arm/Kconfig                             | 1 +
   arch/arm64/include/asm/pgtable.h             | 2 --
   arch/csky/include/asm/pgtable.h              | 1 -
   arch/hexagon/include/asm/pgtable.h           | 3 ---
   arch/ia64/include/asm/pgtable.h              | 1 -
   arch/m68k/include/asm/pgtable_mm.h           | 1 -
   arch/microblaze/include/asm/pgtable.h        | 2 --
   arch/mips/include/asm/pgtable-32.h           | 1 -
   arch/mips/include/asm/pgtable-64.h           | 1 -
   arch/nds32/Kconfig                           | 1 +
   arch/nios2/include/asm/pgtable.h             | 2 --
   arch/openrisc/include/asm/pgtable.h          | 1 -
   arch/parisc/include/asm/pgtable.h            | 2 --
   arch/powerpc/include/asm/book3s/pgtable.h    | 1 -
   arch/powerpc/include/asm/nohash/32/pgtable.h | 1 -
   arch/powerpc/include/asm/nohash/64/pgtable.h | 2 --
   arch/riscv/include/asm/pgtable.h             | 2 --
   arch/s390/include/asm/pgtable.h              | 2 --
   arch/sh/include/asm/pgtable.h                | 2 --
   arch/sparc/include/asm/pgtable_32.h          | 1 -
   arch/sparc/include/asm/pgtable_64.h          | 3 ---
   arch/um/include/asm/pgtable-2level.h         | 1 -
   arch/um/include/asm/pgtable-3level.h         | 1 -
   arch/x86/include/asm/pgtable_types.h         | 2 --
   arch/xtensa/include/asm/pgtable.h            | 1 -
   include/linux/mm.h                           | 4 ++++
   mm/Kconfig                                   | 4 ++++
   29 files changed, 10 insertions(+), 43 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8ba434287387..47098ccd715e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -46,6 +46,10 @@ extern int sysctl_page_lock_unfairness;
     void init_mm_internals(void);
   +#ifndef ARCH_HAS_FIRST_USER_ADDRESS

I guess you didn't test it ..... :)

In fact I did :) Though just booted it on arm64 and cross compiled on
multiple others platforms.

quoted

should be #ifndef CONFIG_ARCH_HAS_FIRST_USER_ADDRESS

Right, meant that instead.

quoted

quoted

+#define FIRST_USER_ADDRESS    0UL
+#endif

But why do we need a config option at all for that ?

Why not just:

#ifndef FIRST_USER_ADDRESS
#define FIRST_USER_ADDRESS    0UL
#endif

This sounds simpler. But just wondering, would not there be any possibility
of build problems due to compilation sequence between arch and generic code ?

For sure it has to be addresses carefully, but there are already a lot of stuff like that around 
pgtables.h

For instance, pte_offset_kernel() has a generic definition in linux/pgtables.h based on whether it 
is already defined or not.

Taking into account that FIRST_USER_ADDRESS is today in the architectures's asm/pgtables.h, I think 
putting the fallback definition in linux/pgtable.h would do the trick.