Hi Dave, On 6/24/20 7:36 PM, Dave Martin wrote: > 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> > > --- > > Since v2: > > * Clarify that the arg2 enumeration for PR_SVE_SET_VL applies to the > bith _other than_ the PR_SVE_VL_LEN_MASK bits, rather than to all the > bits. > > * Clarify return value semantics for PR_SVE_SET_VL, to highlight that > there is no PR_SVE_SET_VL_ONEXEC in the return value and refer to > PR_SVE_GET_VL for the rest of the definition. Also clarify when the > vector length given in the return value actually takes effect. > > * Reorder some documentation cross-references to avoid ambiguity about > what they apply to. Nicely written patch! I've applied locally, but won't push just yet, to allow for some reviews/acks to come in. Thanks, Michael > --- > man2/prctl.2 | 170 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 170 insertions(+) > > diff --git a/man2/prctl.2 b/man2/prctl.2 > index 88b791b..46ea9d2 100644 > --- a/man2/prctl.2 > +++ b/man2/prctl.2 > @@ -1370,6 +1370,158 @@ 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 "(int) arg2" . > +Arguments > +.IR arg3 ", " arg4 " and " arg5 > +are ignored. > +.IP > +The bits of > +.I arg2 > +corresponding to > +.B PR_SVE_VL_LEN_MASK > +must be set to the desired vector length in bytes. > +This is interpreted as an upper bound: > +the kernel will select the greatest available vector length > +that does not exceed the value specified. > +In particular, specifying > +.B SVE_VL_MAX > +(defined in > +.I <asm/sigcontext.h>) > +for the > +.B PR_SVE_VL_LEN_MASK > +bits requests the maximum supported vector length. > +.IP > +In addition, the other bits of > +.I arg2 > +must be set to one of the following combinations of flags: > +.RS > +.TP > +.B 0 > +Perform the change immediately. > +At the next > +.BR execve (2) > +in the thread, > +the vector length will be reset to the value configured in > +.IR /proc/sys/abi/sve_default_vector_length . > +.TP > +.B PR_SVE_VL_INHERIT > +Perform the change immediately. > +Subsequent > +.BR execve (2) > +calls will preserve the new vector length. > +.TP > +.B PR_SVE_SET_VL_ONEXEC > +Defer the change, so that it is performed at the next > +.BR execve (2) > +in the thread. > +Further > +.BR execve (2) > +calls will reset the vector length to the value configured in > +.IR /proc/sys/abi/sve_default_vector_length . > +.TP > +.B "PR_SVE_SET_VL_ONEXEC | PR_SVE_VL_INHERIT" > +Defer the change, so that it is performed at the next > +.BR execve (2) > +in the thread. > +Further > +.BR execve (2) > +calls will preserve the new vector length. > +.RE > +.IP > +In all cases, > +any previously pending deferred change is canceled. > +.IP > +The call fails with error > +.B EINVAL > +if SVE is not supported on the platform, if > +.I arg2 > +is unrecognized or invalid, or the value in the bits of > +.I arg2 > +corresponding to > +.B PR_SVE_VL_LEN_MASK > +is outside the range > +.BR SVE_VL_MIN .. SVE_VL_MAX > +or is not a multiple of 16. > +.IP > +On success, > +a nonnegative value is returned that describes the > +.I selected > +configuration. > +If > +.B PR_SVE_SET_VL_ONEXEC > +was included in > +.IR arg2 , > +then the configuration described by the return value > +will take effect at the next > +.BR execve (). > +Otherwise, the configuration is already in effect when the > +.B PR_SVE_SET_VL > +call returns. > +In either case, the value is encoded in the same way as the return value of > +.BR PR_SVE_GET_VL . > +Note that there is no explicit flag in the return value > +corresponding to > +.BR PR_SVE_SET_VL_ONEXEC . > +.IP > +The configuration (including any pending deferred change) > +is inherited across > +.BR fork (2) > +and > +.BR clone (2). > +.IP > +For more information, see the kernel source file > +.I Documentation/arm64/sve.rst > +.\"commit b693d0b372afb39432e1c49ad7b3454855bc6bed > +(or > +.I Documentation/arm64/sve.txt > +before Linux 5.3). > +.IP > +.B Warning: > +Because the compiler or run-time environment > +may be using SVE, using this call without the > +.B PR_SVE_SET_VL_ONEXEC > +flag may crash the calling process. > +The conditions for using it safely are complex and system-dependent. > +Don't use it unless you really know what you are doing. > +.\" 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. > +.IP > +Arguments > +.IR arg2 ", " arg3 ", " arg4 " and " arg5 > +are ignored. > +.IP > +Providing that the kernel and platform support SVE > +this operation always succeeds, > +returning a nonnegative value that 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 to determine whether there is > +a pending vector length change that has not yet taken effect. > +.IP > +For more information, see the kernel source file > +.I Documentation/arm64/sve.rst > +.\"commit b693d0b372afb39432e1c49ad7b3454855bc6bed > +(or > +.I Documentation/arm64/sve.txt > +before Linux 5.3). > .\" > .\" prctl PR_TASK_PERF_EVENTS_DISABLE > .TP > @@ -1613,6 +1765,8 @@ 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 , > @@ -1904,6 +2058,22 @@ See the description of > .B PR_PAC_RESET_KEYS > above for details. > .TP > +.B EINVAL > +.I option > +is > +.B PR_SVE_SET_VL > +and the arguments are invalid or unsupported, > +or SVE is not available on this platform. > +See the description of > +.B PR_SVE_SET_VL > +above for details. > +.TP > +.B EINVAL > +.I option > +is > +.B PR_SVE_GET_VL > +and SVE is not available on this platform. > +.TP > .B ENODEV > .I option > was > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
