Minki/linux
1
0
Fork 1
mirror of https://github.com/torvalds/linux.git synced 2024-12-27 05:11:48 +00:00
Code Issues Packages Projects Releases Wiki Activity

arm64/sve: Add sysctl to set the default vector length for new processes

Browse Source 
Because of the effect of SVE on the size of the signal frame, the
default vector length used for new processes involves a tradeoff
between performance of SVE-enabled software on the one hand, and
reliability of non-SVE-aware software on the other hand.

For this reason, the best choice depends on the repertoire of
userspace software in use and is thus best left up to distro
maintainers, sysadmins and developers.

If CONFIG_SYSCTL and CONFIG_PROC_SYSCTL are enabled, this patch
exposes the default vector length in
/proc/sys/abi/sve_default_vector_length, where boot scripts or the
adventurous can poke it.

In common with other arm64 ABI sysctls, this control is currently
global: setting it requires CAP_SYS_ADMIN in the root user
namespace, but the value set is effective for subsequent execs in
all namespaces.  The control only affects _new_ processes, however:
changing it does not affect the vector length of any existing
process.

The intended usage model is that if userspace is known to be fully
SVE-tolerant (or a developer is curious to find out) then this
parameter can be cranked up during system startup.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Dave Martin 2017-10-31 15:51:15 +00:00 committed by Will Deacon
parent 2d2123bc7c
commit 4ffa09a939
1 changed files with 61 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

62
arch/arm64/kernel/fpsimd.c
View File

@ -37,6 +37,7 @@
#include <linux/sched/task_stack.h>
#include <linux/signal.h>
#include <linux/slab.h>
#include <linux/sysctl.h>
#include <asm/fpsimd.h>
#include <asm/cputype.h>
@ -335,6 +336,65 @@ static unsigned int find_supported_vector_length(unsigned int vl)
return sve_vl_from_vq(bit_to_vq(bit));
}
#ifdef CONFIG_SYSCTL
static int sve_proc_do_default_vl(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos)
{
int ret;
int vl = sve_default_vl;
struct ctl_table tmp_table = {
.data = &vl,
.maxlen = sizeof(vl),
};
ret = proc_dointvec(&tmp_table, write, buffer, lenp, ppos);
if (ret || !write)
return ret;
/* Writing -1 has the special meaning "set to max": */
if (vl == -1) {
/* Fail safe if sve_max_vl wasn't initialised */
if (WARN_ON(!sve_vl_valid(sve_max_vl)))
vl = SVE_VL_MIN;
else
vl = sve_max_vl;
goto chosen;
}
if (!sve_vl_valid(vl))
return -EINVAL;
vl = find_supported_vector_length(vl);
chosen:
sve_default_vl = vl;
return 0;
}
static struct ctl_table sve_default_vl_table[] = {
{
.procname = "sve_default_vector_length",
.mode = 0644,
.proc_handler = sve_proc_do_default_vl,
},
{ }
};
static int __init sve_sysctl_init(void)
{
if (system_supports_sve())
if (!register_sysctl("abi", sve_default_vl_table))
return -EINVAL;
return 0;
}
#else /* ! CONFIG_SYSCTL */
static int __init sve_sysctl_init(void) { return 0; }
#endif /* ! CONFIG_SYSCTL */
#define ZREG(sve_state, vq, n) ((char *)(sve_state) + \
(SVE_SIG_ZREG_OFFSET(vq, n) - SVE_SIG_REGS_OFFSET))
@ -1209,6 +1269,6 @@ static int __init fpsimd_init(void)
if (!(elf_hwcap & HWCAP_ASIMD))
pr_notice("Advanced SIMD is not implemented\n");
return 0;
return sve_sysctl_init();
}
late_initcall(fpsimd_init);