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1
Linux Support for
ARM LPAE
Catalin Marinas
ELC Europe 2011
2
Agenda
!
Introduction
!
Classic ARM MMU
!
Classic ARM MMU Limitations
!
ARM LPAE Features
!
ARM LPAE and Virtualisation
!
Linux and ARM LPAE
!
Current Status and Future Developments
3
Introduction
!
Early ARM systems required only a few MBs of RAM
!
More and more complex smart-phones requiring 100s MB or
even GBs of RAM
!
32-bit physical addresses impose a 4GB hard limit
!
It’s not all about RAM
!
Peripherals
!
Flash memory
!
System ROM
!
(Mobile) virtualisation requires even more RAM
!
But not necessarily at the Guest OS level
!
ARM LPAE support for Linux developed within ARM Ltd.
!
First patches posted on LKML – October 2010
4
Classic ARM MMU
!
32-bit physical address space
!
2-level translation tables
!
Pointed to by TTBR0 (user mappings) and TTBR1 (kernel mappings
but with restrictions to the user/kernel memory split)
!
32-bit page table entries
!
1
st
level contains 4096 entries (4 pages for PGD)
!
1MB section per entry or
!
Pointer to a 2
nd
level table
!
Implementation-defined 16MB supersections
!
2
nd
level contains 256 entries pointing to 4KB page each
!
1KB per 2
nd
level page table
!
ARMv6/v7 introduced TEX remapping
!
Memory type becomes a 3-bit index
5
Classic ARM MMU (cont’d)
!
Other features
!
XN (eXecute Never) bit
!
Different memory types: Normal (cacheable and non-cacheable),
Device, Strongly Ordered
!
Shareability attributes for SMP systems
!
ASID-tagged TLB (ARMv6 onwards)
!
Avoids TLB flushing at context switch
!
8-bit ASID value assigned to an
mm_struct
!
Dynamically allocated (there can be more than 256 processes)
剩余21页未读,继续阅读
资源评论
- ComputeGeneral2017-12-09可以作为辅助材料,主要还是看ARM的文档
- itoyokoda2014-03-04有一定的介绍关于LPAE,但是关于内部机制好像并不是很详细
- fwdflywl2015-11-21对LPAE的介绍不错,值得一看.
howtwell
- 粉丝: 3
- 资源: 14
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