mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-11-16 16:54:20 +08:00
s390/docs: Fix the documentation of the address spaces
The information about the address spaces was completely outdated, since
the usage of the address spaces changed quite a bit since the early days.
This patch now updates the information about the usage of the address
spaces, mostly by using the description from Heiko's patch "rework uaccess
code - fix locking issues" (457f218095).
Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Thomas Huth
Martin Schwidefsky
parent
eaf785d51d
commit
b195562311
@ -114,28 +114,25 @@ s/390 z/Architecture
|
||||
|
||||
16-17 16-17 Address Space Control
|
||||
|
||||
00 Primary Space Mode when DAT on
|
||||
The linux kernel currently runs in this mode, CR1 is affiliated with
|
||||
this mode & points to the primary segment table origin etc.
|
||||
00 Primary Space Mode:
|
||||
The register CR1 contains the primary address-space control ele-
|
||||
ment (PASCE), which points to the primary space region/segment
|
||||
table origin.
|
||||
|
||||
01 Access register mode this mode is used in functions to
|
||||
copy data between kernel & user space.
|
||||
01 Access register mode
|
||||
|
||||
10 Secondary space mode not used in linux however CR7 the
|
||||
register affiliated with this mode is & this & normally
|
||||
CR13=CR7 to allow us to copy data between kernel & user space.
|
||||
We do this as follows:
|
||||
We set ar2 to 0 to designate its
|
||||
affiliated gpr ( gpr2 )to point to primary=kernel space.
|
||||
We set ar4 to 1 to designate its
|
||||
affiliated gpr ( gpr4 ) to point to secondary=home=user space
|
||||
& then essentially do a memcopy(gpr2,gpr4,size) to
|
||||
copy data between the address spaces, the reason we use home space for the
|
||||
kernel & don't keep secondary space free is that code will not run in
|
||||
secondary space.
|
||||
10 Secondary Space Mode:
|
||||
The register CR7 contains the secondary address-space control
|
||||
element (SASCE), which points to the secondary space region or
|
||||
segment table origin.
|
||||
|
||||
11 Home Space Mode all user programs run in this mode.
|
||||
it is affiliated with CR13.
|
||||
11 Home Space Mode:
|
||||
The register CR13 contains the home space address-space control
|
||||
element (HASCE), which points to the home space region/segment
|
||||
table origin.
|
||||
|
||||
See "Address Spaces on Linux for s/390 & z/Architecture" below
|
||||
for more information about address space usage in Linux.
|
||||
|
||||
18-19 18-19 Condition codes (CC)
|
||||
|
||||
@ -249,9 +246,9 @@ currently 4TB of physical memory currently on z/Architecture.
|
||||
Address Spaces on Linux for s/390 & z/Architecture
|
||||
==================================================
|
||||
|
||||
Our addressing scheme is as follows
|
||||
|
||||
Our addressing scheme is basically as follows:
|
||||
|
||||
Primary Space Home Space
|
||||
Himem 0x7fffffff 2GB on s/390 ***************** ****************
|
||||
currently 0x3ffffffffff (2^42)-1 * User Stack * * *
|
||||
on z/Architecture. ***************** * *
|
||||
@ -264,9 +261,46 @@ on z/Architecture. ***************** * *
|
||||
* Sections * * *
|
||||
0x00000000 ***************** ****************
|
||||
|
||||
This also means that we need to look at the PSW problem state bit
|
||||
or the addressing mode to decide whether we are looking at
|
||||
user or kernel space.
|
||||
This also means that we need to look at the PSW problem state bit and the
|
||||
addressing mode to decide whether we are looking at user or kernel space.
|
||||
|
||||
User space runs in primary address mode (or access register mode within
|
||||
the vdso code).
|
||||
|
||||
The kernel usually also runs in home space mode, however when accessing
|
||||
user space the kernel switches to primary or secondary address mode if
|
||||
the mvcos instruction is not available or if a compare-and-swap (futex)
|
||||
instruction on a user space address is performed.
|
||||
|
||||
When also looking at the ASCE control registers, this means:
|
||||
|
||||
User space:
|
||||
- runs in primary or access register mode
|
||||
- cr1 contains the user asce
|
||||
- cr7 contains the user asce
|
||||
- cr13 contains the kernel asce
|
||||
|
||||
Kernel space:
|
||||
- runs in home space mode
|
||||
- cr1 contains the user or kernel asce
|
||||
-> the kernel asce is loaded when a uaccess requires primary or
|
||||
secondary address mode
|
||||
- cr7 contains the user or kernel asce, (changed with set_fs())
|
||||
- cr13 contains the kernel asce
|
||||
|
||||
In case of uaccess the kernel changes to:
|
||||
- primary space mode in case of a uaccess (copy_to_user) and uses
|
||||
e.g. the mvcp instruction to access user space. However the kernel
|
||||
will stay in home space mode if the mvcos instruction is available
|
||||
- secondary space mode in case of futex atomic operations, so that the
|
||||
instructions come from primary address space and data from secondary
|
||||
space
|
||||
|
||||
In case of KVM, the kernel runs in home space mode, but cr1 gets switched
|
||||
to contain the gmap asce before the SIE instruction gets executed. When
|
||||
the SIE instruction is finished, cr1 will be switched back to contain the
|
||||
user asce.
|
||||
|
||||
|
||||
Virtual Addresses on s/390 & z/Architecture
|
||||
===========================================
|
||||
|
||||
Loading…
Reference in New Issue
Block a user