man2/s390_guarded_storage.2

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  25 .TH S390_GUARDED_STORAGE 2 2019-03-06 "Linux Programmer's Manual"
  26 .SH NAME
  27 s390_guarded_storage \- operations with z/Architecture guarded storage facility
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <asm/guarded_storage.h>
  31 .PP
  32 .BI "int s390_guarded_storage(int " command ", struct gs_cb *" gs_cb ");"
  33 .fi
  34 .SH DESCRIPTION
  35 The
  36 .BR s390_guarded_storage ()
  37 system call enables the use of the Guarded Storage Facility
  38 (a z/Architecture-specific feature) for user-space processes.
  39 .PP
  40 .\" The description is based on
  41 .\" http://www-05.ibm.com/de/linux-on-z-ws-us/agenda/pdfs/8_-_Linux_Whats_New_-_Stefan_Raspl.pdf
  42 .\" and "z/Architecture Principles of Operation" obtained from
  43 .\" http://publibfi.boulder.ibm.com/epubs/pdf/dz9zr011.pdf
  44 The guarded storage facility is a hardware feature that allows marking up to
  45 64 memory regions (as of z14) as guarded;
  46 reading a pointer with a newly introduced "Load Guarded" (LGG)
  47 or "Load Logical and Shift Guarded" (LLGFSG) instructions will cause
  48 a range check on the loaded value and invoke a (previously set up)
  49 user-space handler if one of the guarded regions is affected.
  50 .PP
  51 The
  52 .\" The command description is copied from v4.12-rc1~139^2~56^2 commit message
  53 .I command
  54 argument indicates which function to perform.
  55 The following commands are supported:
  56 .TP
  57 .B GS_ENABLE
  58 Enable the guarded storage facility for the calling task.
  59 The initial content of the guarded storage control block will be all zeros.
  60 After enablement, user-space code can use the "Load Guarded Storage
  61 Controls" (LGSC) instruction (or the
  62 .BR load_gs_cb ()
  63 function wrapper provided in the
  64 .I asm/guarded_storage.h
  65 header) to load an arbitrary control block.
  66 While a task is enabled, the kernel will save and restore the calling content
  67 of the guarded storage registers on context switch.
  68 .TP
  69 .B GS_DISABLE
  70 Disables the use of the guarded storage facility for the calling task.
  71 The kernel will cease to save and restore the content of the guarded storage
  72 registers, the task-specific content of these registers is lost.
  73 .TP
  74 .B GS_SET_BC_CB
  75 Set a broadcast guarded storage control block to the one provided in the
  76 .I gs_cb
  77 argument.
  78 This is called per thread and associates a specific guarded storage control
  79 block with the calling task.
  80 This control block will be used in the broadcast command
  81 .BR GS_BROADCAST .
  82 .TP
  83 .B GS_CLEAR_BC_CB
  84 Clears the broadcast guarded storage control block.
  85 The guarded storage control block will no longer have the association
  86 established by the
  87 .B GS_SET_BC_CB
  88 command.
  89 .TP
  90 .B GS_BROADCAST
  91 Sends a broadcast to all thread siblings of the calling task.
  92 Every sibling that has established a broadcast guarded storage control block
  93 will load this control block and will be enabled for guarded storage.
  94 The broadcast guarded storage control block is consumed; a second broadcast
  95 without a refresh of the stored control block with
  96 .B GS_SET_BC_CB
  97 will not have any effect.
  98 .PP
  99 The
 100 .I gs_cb
 101 argument specifies the address of a guarded storage control block structure
 102 and is currently used only by the
 103 .B GS_SET_BC_CB
 104 command; all other aforementioned commands ignore this argument.
 105 .SH RETURN VALUE
 106 On success, the return value of
 107 .BR s390_guarded_storage ()
 108 is 0.
 109 .PP
 110 On error, \-1 is returned, and
 111 .IR errno
 112 is set appropriately.
 113 .SH ERRORS
 114 .TP
 115 .B EFAULT
 116 .I command
 117 was
 118 .BR GS_SET_BC_CB
 119 and the copying of the guarded storage control block structure pointed by the
 120 .I gs_cb
 121 argument has failed.
 122 .TP
 123 .B EINVAL
 124 The value provided in the
 125 .I command
 126 argument was not valid.
 127 .TP
 128 .B ENOMEM
 129 .I command
 130 was one of
 131 .BR GS_ENABLE " or " GS_SET_BC_CB ,
 132 and the allocation of a new guarded storage control block has failed.
 133 .TP
 134 .B EOPNOTSUPP
 135 The guarded storage facility is not supported by the hardware.
 136 .SH VERSIONS
 137 .\" 916cda1aa1b412d7cf2991c3af7479544942d121, v4.12-rc1~139^2~56^2
 138 This system call is available since Linux 4.12.
 139 .SH CONFORMING TO
 140 This Linux-specific system call is available only on the s390 architecture.
 141 .PP
 142 The guarded storage facility is available beginning with System z14.
 143 .SH NOTES
 144 Glibc does not provide a wrapper for this system call, use
 145 .BR syscall (2)
 146 to call it.
 147 .PP
 148 The description of the guarded storage facility along with related
 149 instructions and Guarded Storage Control Block and
 150 Guarded Storage Event Parameter List structure layouts
 151 is available in "z/Architecture Principles of Operations"
 152 beginning from the twelfth edition.
 153 .PP
 154 The
 155 .I gs_cb
 156 structure has a field
 157 .I gsepla
 158 (Guarded Storage Event Parameter List Address), which is a user-space pointer
 159 to a Guarded Storage Event Parameter List structure
 160 (that contains the address
 161 of the aforementioned event handler in the
 162 .I gseha
 163 field), and its layout is available as a
 164 .B gs_epl
 165 structure type definition in the
 166 .I asm/guarded_storage.h
 167 header.
 168 .\" .PP
 169 .\" For the example of using the guarded storage facility, see
 170 .\" .UR https://developer.ibm.com/javasdk/2017/09/25/concurrent-scavenge-using-guarded-storage-facility-works/
 171 .\" the article with the description of its usage in the Java Garbage Collection
 172 .\" .UE
 173 .PP
 174 .SH SEE ALSO
 175 .BR syscall (2)