Add documentation for the the PR_SVE_SET_VL and PR_SVE_GET_VL prctls added in Linux 4.15 for arm64. Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> --- I wrote the SVE support originally, so I probably have this one halfway right. The explantion added is not exhaustive, but I didn't want it to be too verbose. I may trim it a bit and move the detail to a dedicated page later on, but this is better than nothing in the meantime. --- man2/prctl.2 | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 112 insertions(+) diff --git a/man2/prctl.2 b/man2/prctl.2 index 7f511d2..dd16227 100644 --- a/man2/prctl.2 +++ b/man2/prctl.2 @@ -1291,6 +1291,104 @@ call failing with the error .BR ENXIO . For further details, see the kernel source file .IR Documentation/admin-guide/kernel-parameters.txt . +.\" prctl PR_SVE_SET_VL +.\" commit 2d2123bc7c7f843aa9db87720de159a049839862 +.\" linux-5.6/Documentation/arm64/sve.rst +.TP +.BR PR_SVE_SET_VL " (since Linux 4.15, only on arm64)" +Configure the thread's SVE vector length, +as specified by +.IR arg2 . +Arguments +.IR arg3 ", " arg4 " and " arg5 +are ignored. +.IP +The bits of +.I arg2 +corresponding to +.B SVE_VL_LEN_MASK +must be set to the desired vector length in bytes. +In addition, +.I arg2 +may include zero or more of the following flags: +.RS +.TP +.B PR_SVE_VL_INHERIT +Inherit the configured vector length across +.BR execve (2). +.TP +.B PR_SVE_SET_VL_ONEXEC +Defer the change until the next +.BR execve (2) +in this thread. +If +.B PR_SVE_VL_INHERIT +is also included in +.IR arg2 , +it takes effect +.I after +this deferred change. +.RE +.IP +On success, the vector length and flags are set as requested, +and any deferred change that was pending immediately before the +.B PR_SVE_SET_VL +call is canceled. +If +.B PR_SVE_SET_VL_ONEXEC +was included in +.IR arg2 , +the returned value describes the configuration +scheduled to take effect at the next +.BR execve (2). +Otherwise, the effect is immediate and +the returned value describes the new configuration. +The returned value is encoded in the same way as the return value of +.BR PR_SVE_GET_VL . +.IP +If neither of the above flags is included in +.IR arg2 , +a subsequent +.BR execve (2) +resets the vector length to the default value configured in +.IR /proc/sys/abi/sve_default_vector_length . +.IP +The actual vector length configured by this operation +is the greatest vector length supported by the platform +that does not exceed +.I arg2 +& +.BR PR_SVE_VL_LEN_MASK . +.IP +The configuration (including any pending deferred change) +is inherited across +.BR fork (2) +and +.BR clone (2). +.\" prctl PR_SVE_GET_VL +.TP +.BR PR_SVE_GET_VL " (since Linux 4.15, only on arm64)" +Get the thread's current SVE vector length configuration, +as configured by +.BR PR_SVE_SET_VL . +.IP +If successful, the return value describes the +.I current +configuration. +The bits corresponding to +.B PR_SVE_VL_LEN_MASK +contain the currently configured vector length in bytes. +The bit corresponding to +.B PR_SVE_VL_INHERIT +indicates whether the vector length will be inherited +across +.BR execve (2). +.IP +Note that there is no way determine whether there is +a pending vector length change that has not yet taken effect. +.IP +Providing that the kernel and platform support SVE, +this operation always succeeds. .\" .\" prctl PR_TASK_PERF_EVENTS_DISABLE .TP @@ -1534,6 +1632,8 @@ On success, .BR PR_GET_NO_NEW_PRIVS , .BR PR_GET_SECUREBITS , .BR PR_GET_SPECULATION_CTRL , +.BR PR_SVE_GET_VL , +.BR PR_SVE_SET_VL , .BR PR_GET_THP_DISABLE , .BR PR_GET_TIMING , .BR PR_GET_TIMERSLACK , @@ -1817,6 +1917,18 @@ and unused arguments to .BR prctl () are not 0. .TP +.B EINVAL +.I option +was +.B PR_SVE_SET_VL +and +.I arg2 +contains invalid flags, or +.I arg2 +& +.B SVE_VL_LEN_MASK +is not a valid vector length. +.TP .B ENODEV .I option was -- 2.1.4
