mirror of https://github.com/mkerrisk/man-pages
prctl.2: Add SVE prctls (arm64)
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@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Dave Martin
Michael Kerrisk
parent
27e0d164d9
commit
034f403aa7
170
man2/prctl.2
170
man2/prctl.2
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@ -1370,6 +1370,158 @@ call failing with the error
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.BR ENXIO .
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For further details, see the kernel source file
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.IR Documentation/admin\-guide/kernel\-parameters.txt .
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.\" prctl PR_SVE_SET_VL
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.\" commit 2d2123bc7c7f843aa9db87720de159a049839862
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.\" linux-5.6/Documentation/arm64/sve.rst
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.TP
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.BR PR_SVE_SET_VL " (since Linux 4.15, only on arm64)"
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Configure the thread's SVE vector length,
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as specified by
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.IR "(int) arg2" .
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Arguments
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.IR arg3 ", " arg4 " and " arg5
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are ignored.
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.IP
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The bits of
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.I arg2
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corresponding to
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.B PR_SVE_VL_LEN_MASK
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must be set to the desired vector length in bytes.
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This is interpreted as an upper bound:
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the kernel will select the greatest available vector length
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that does not exceed the value specified.
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In particular, specifying
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.B SVE_VL_MAX
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(defined in
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.I <asm/sigcontext.h>)
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for the
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.B PR_SVE_VL_LEN_MASK
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bits requests the maximum supported vector length.
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.IP
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In addition, the other bits of
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.I arg2
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must be set to one of the following combinations of flags:
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.RS
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.TP
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.B 0
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Perform the change immediately.
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At the next
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.BR execve (2)
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in the thread,
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the vector length will be reset to the value configured in
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.IR /proc/sys/abi/sve_default_vector_length .
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.TP
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.B PR_SVE_VL_INHERIT
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Perform the change immediately.
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Subsequent
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.BR execve (2)
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calls will preserve the new vector length.
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.TP
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.B PR_SVE_SET_VL_ONEXEC
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Defer the change, so that it is performed at the next
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.BR execve (2)
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in the thread.
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Further
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.BR execve (2)
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calls will reset the vector length to the value configured in
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.IR /proc/sys/abi/sve_default_vector_length .
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.TP
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.B "PR_SVE_SET_VL_ONEXEC | PR_SVE_VL_INHERIT"
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Defer the change, so that it is performed at the next
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.BR execve (2)
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in the thread.
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Further
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.BR execve (2)
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calls will preserve the new vector length.
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.RE
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.IP
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In all cases,
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any previously pending deferred change is canceled.
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.IP
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The call fails with error
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.B EINVAL
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if SVE is not supported on the platform, if
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.I arg2
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is unrecognized or invalid, or the value in the bits of
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.I arg2
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corresponding to
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.B PR_SVE_VL_LEN_MASK
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is outside the range
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.BR SVE_VL_MIN .. SVE_VL_MAX
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or is not a multiple of 16.
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.IP
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On success,
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a nonnegative value is returned that describes the
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.I selected
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configuration.
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If
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.B PR_SVE_SET_VL_ONEXEC
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was included in
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.IR arg2 ,
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then the configuration described by the return value
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will take effect at the next
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.BR execve ().
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Otherwise, the configuration is already in effect when the
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.B PR_SVE_SET_VL
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call returns.
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In either case, the value is encoded in the same way as the return value of
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.BR PR_SVE_GET_VL .
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Note that there is no explicit flag in the return value
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corresponding to
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.BR PR_SVE_SET_VL_ONEXEC .
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.IP
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The configuration (including any pending deferred change)
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is inherited across
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.BR fork (2)
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and
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.BR clone (2).
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.IP
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For more information, see the kernel source file
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.I Documentation/arm64/sve.rst
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.\"commit b693d0b372afb39432e1c49ad7b3454855bc6bed
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(or
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.I Documentation/arm64/sve.txt
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before Linux 5.3).
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.IP
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.B Warning:
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Because the compiler or run-time environment
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may be using SVE, using this call without the
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.B PR_SVE_SET_VL_ONEXEC
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flag may crash the calling process.
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The conditions for using it safely are complex and system-dependent.
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Don't use it unless you really know what you are doing.
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.\" prctl PR_SVE_GET_VL
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.TP
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.BR PR_SVE_GET_VL " (since Linux 4.15, only on arm64)"
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Get the thread's current SVE vector length configuration.
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.IP
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Arguments
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.IR arg2 ", " arg3 ", " arg4 " and " arg5
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are ignored.
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.IP
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Providing that the kernel and platform support SVE
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this operation always succeeds,
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returning a nonnegative value that describes the
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.I current
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configuration.
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The bits corresponding to
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.B PR_SVE_VL_LEN_MASK
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contain the currently configured vector length in bytes.
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The bit corresponding to
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.B PR_SVE_VL_INHERIT
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indicates whether the vector length will be inherited
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across
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.BR execve (2).
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.IP
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Note that there is no way to determine whether there is
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a pending vector length change that has not yet taken effect.
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.IP
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For more information, see the kernel source file
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.I Documentation/arm64/sve.rst
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.\"commit b693d0b372afb39432e1c49ad7b3454855bc6bed
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(or
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.I Documentation/arm64/sve.txt
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before Linux 5.3).
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.\"
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.\" prctl PR_TASK_PERF_EVENTS_DISABLE
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.TP
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@ -1613,6 +1765,8 @@ On success,
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.BR PR_GET_NO_NEW_PRIVS ,
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.BR PR_GET_SECUREBITS ,
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.BR PR_GET_SPECULATION_CTRL ,
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.BR PR_SVE_GET_VL ,
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.BR PR_SVE_SET_VL ,
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.BR PR_GET_THP_DISABLE ,
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.BR PR_GET_TIMING ,
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.BR PR_GET_TIMERSLACK ,
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@ -1904,6 +2058,22 @@ See the description of
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.B PR_PAC_RESET_KEYS
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above for details.
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.TP
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.B EINVAL
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.I option
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is
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.B PR_SVE_SET_VL
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and the arguments are invalid or unsupported,
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or SVE is not available on this platform.
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See the description of
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.B PR_SVE_SET_VL
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above for details.
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.TP
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.B EINVAL
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.I option
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is
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.B PR_SVE_GET_VL
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and SVE is not available on this platform.
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.TP
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.B ENODEV
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.I option
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was
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