diff options
Diffstat (limited to 'Documentation/s390')
| -rw-r--r-- | Documentation/s390/Debugging390.txt | 88 |
1 files changed, 61 insertions, 27 deletions
diff --git a/Documentation/s390/Debugging390.txt b/Documentation/s390/Debugging390.txt index 462321c..2120eec 100644 --- a/Documentation/s390/Debugging390.txt +++ b/Documentation/s390/Debugging390.txt @@ -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. - - 01 Access register mode this mode is used in functions to - copy data between kernel & user space. - - 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. - - 11 Home Space Mode all user programs run in this mode. - it is affiliated with CR13. + 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 + + 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: + 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 =========================================== |
