[RFC PATCH 06/10] arm64/sve: Disallow VL setting for individual threads by default
Dave Martin <[email protected]>
| Newsgroups | gmane.linux.kernel.cross-arch,gmane.linux.ports.arm.kernel,gmane.comp.lib.glibc.alpha,gmane.comp.gdb.devel |
|---|---|
| Message-ID | <[email protected]> |
General-purpose code in userspace is not expected to work correctly if multiple threads are allowed to run concurrently with different vector lengths in a single process. This patch adds an explicit flag PR_SVE_SET_VL_THREAD to request this behaviour. Without the flag, vector length setting is permitted only for a single-threaded process (which matches the expected usage model of setting the vector length at process startup). Signed-off-by: Dave Martin <[email protected]> --- arch/arm64/kernel/fpsimd.c | 12 +++++++++++- include/uapi/linux/prctl.h | 1 + 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 5f2c24a..32caca3 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -21,6 +21,7 @@ #include <linux/cpu_pm.h> #include <linux/kernel.h> #include <linux/init.h> +#include <linux/prctl.h> #include <linux/sched.h> #include <linux/signal.h> #include <linux/hardirq.h> @@ -498,8 +499,17 @@ int sve_set_vector_length(struct task_struct *task, { BUG_ON(task == current && preemptible()); + /* + * To avoid accidents, forbid setting for individual threads of a + * multithreaded process. User code that knows what it's doing can + * pass PR_SVE_SET_VL_THREAD to override this restriction: + */ + if (!(flags & PR_SVE_SET_VL_THREAD) && get_nr_threads(task) != 1) + return -EINVAL; + + flags &= ~(unsigned long)PR_SVE_SET_VL_THREAD; if (flags) - return -EINVAL; /* No flags defined yet */ + return -EINVAL; /* No other flags defined yet */ if (!sve_vl_valid(vl)) return -EINVAL; diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index e32e2da..c55530b 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -199,6 +199,7 @@ struct prctl_mm_map { /* arm64 Scalable Vector Extension controls */ #define PR_SVE_SET_VL 48 /* set task vector length */ +# define PR_SVE_SET_VL_THREAD (1 << 1) /* set just this thread */ #define PR_SVE_GET_VL 49 /* get task vector length */ #endif /* _LINUX_PRCTL_H */ -- 2.1.4