Hi Dave, I've not applied this patch yet, in case you want to make some changes in response to Will's comments. I think all of the rest of the patches in the series are now applied (and pushed to master). Thanks, Michael On 5/27/20 11:17 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 v1: > > * Minor rewordings and typo fixes. > > * Fix typo'd #define names. > > * Add type annotation for PR_SVE_SET_VL arg2. > > * Clarify return value semantics of PR_SVE_SET_VL > > * Add note to say that the args for PR_SVE_GET_VL are ignored. > > * Note for PR_SVE_SET_VL that the PR_SVE_VL_LEN_MASK field specifies > an upper bound on what vector length to set, not an exact value. > > * Rework PR_SVE_SET_VL arg2 description to enumerate all possible flag > combinations rather than describing the flags independently. > > Coming up with a clear description of each flag that is independent > of the description of the other flag turns out to be hard. > > * In lieu of having a separate man page to cross reference for detailed > guidance, cross-reference the kernel documentation. > > * Avoid confusing cross-reference to PR_SVE_SET_VL when describing the > return value of PR_SVE_GET_VL. > > * Clarify error conditions for PR_SVE_SET_VL and PR_SVE_GET_VL, and > move detail to the individual prctl descriptions to keep related > content close together while minimising duplication. > > * Add safety warning. This is deliberately vague, pending ongoing > discussions with libc folks. > --- > man2/prctl.2 | 160 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 160 insertions(+) > > diff --git a/man2/prctl.2 b/man2/prctl.2 > index cab9915..91df7c8 100644 > --- a/man2/prctl.2 > +++ b/man2/prctl.2 > @@ -1291,6 +1291,148 @@ 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, > +.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, > +which may differ from the current configuration if > +.B PR_SVE_SET_VL_ONEXEC > +was specified. > +The value is encoded in the same way as the return value of > +.BR PR_SVE_GET_VL . > +.IP > +The configuration (including any pending deferred change) > +is inherited across > +.BR fork (2) > +and > +.BR clone (2). > +.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. > +.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_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 > @@ -1534,6 +1676,8 @@ 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 +1961,22 @@ and unused arguments to > .BR prctl () > are not 0. > .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/
