Hi Will,
I have a question about arm pagetable setting in Linux .
From armV6, there is TTBR0 and TTBR1 translation base address registers in
mmu .
But I found linux only use TTBR0 for translation base address ,
Could we use TTBR0 and TTBR1 to split user task and kernel pagetables
(swapper_pg_dir)？
But I found this need set TTBCR.N ,
If PAGE_OFFSET==0xc0000000 , set TTBCR.N=0x2 ,
Will not work , because only ensure 0--0x00FFFFFF MVA use TTBCR0
And other MVA will use TTBCR1 ,
But if we set PAGE_OFFSET==0x80000000 (2GB split ) ,
And set TTBCR.N=0x1 ,
This will make sure user task MVA use TTBCR0 and kernel MVA
Use TTBCR1 , this will make some improvement for the system .
1. Because we don’t need copy kernel first –level pagetables into every
User task’s pagetables and flush tlb (for example fork() a new process).
2. And don’t need handle kernel page fault because that user task’s kernel
Pagetable when it is not set up , need copy again( for example vmalloc()
ioremap() kmap() will change
Kernel pagetables and need update to every task pagetables ) .
3. We even can only allocate 8KB first level pagetables for user task to save
Memorys .
I am not sure if its possible to implement this on cortex-A cpus ?
And if there is some side effects if we use this in linux ?
If possible , I can make a change to do some test .
Thanks for your help .
Yalin.Wang
Software Engineer
OS Kernel&Graphics
Sony Mobile Communications
Tel: +86 10 5966 9819
Phone: 18610323092
Address: No.16 Guangshun South Street, Chaoyang, Beijing, P.R.C.
sonymobile.com
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