To support Vector extension, the series exports variable-length vector registers on the signal frame. However, this potentially breaks abi if processing vector registers is required in the signal handler for old binaries. For example, there is such need if user-level context switch is triggerred via signals[1]. For this reason, it is best to leave a decision to distro maintainers, where the enablement of userspace Vector for new launching programs can be controlled. Developers may also need the switch to experiment with. The parameter is configurable through sysctl interface so a distro may turn off Vector early at init script if the break really happens in the wild. The switch will only take effects on new execve() calls once set. This will not effect existing processes that do not call execve(), nor processes which has been set with a non-default vstate_ctrl by making explicit PR_RISCV_V_SET_CONTROL prctl() calls. Link: https://lore.kernel.org/all/87cz4048rp.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ Signed-off-by: Andy Chiu <andy.chiu@xxxxxxxxxx> Reviewed-by: Greentime Hu <greentime.hu@xxxxxxxxxx> Reviewed-by: Vincent Chen <vincent.chen@xxxxxxxxxx> --- Changelog v20: - Use READ_ONCE to access riscv_v_implicit_uacc (Björn) --- arch/riscv/kernel/vector.c | 33 ++++++++++++++++++++++++++++++++- 1 file changed, 32 insertions(+), 1 deletion(-) diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c index 9bee7a201106..25c7f5c93b00 100644 --- a/arch/riscv/kernel/vector.c +++ b/arch/riscv/kernel/vector.c @@ -184,7 +184,7 @@ void riscv_v_vstate_ctrl_init(struct task_struct *tsk) next = riscv_v_ctrl_get_next(tsk); if (!next) { - if (riscv_v_implicit_uacc) + if (READ_ONCE(riscv_v_implicit_uacc)) cur = PR_RISCV_V_VSTATE_CTRL_ON; else cur = PR_RISCV_V_VSTATE_CTRL_OFF; @@ -247,3 +247,34 @@ long riscv_v_vstate_ctrl_set_current(unsigned long arg) return -EINVAL; } + +#ifdef CONFIG_SYSCTL + +static struct ctl_table riscv_v_default_vstate_table[] = { + { + .procname = "riscv_v_default_allow", + .data = &riscv_v_implicit_uacc, + .maxlen = sizeof(riscv_v_implicit_uacc), + .mode = 0644, + .proc_handler = proc_dobool, + }, + { } +}; + +static int __init riscv_v_sysctl_init(void) +{ + if (has_vector()) + if (!register_sysctl("abi", riscv_v_default_vstate_table)) + return -EINVAL; + return 0; +} + +#else /* ! CONFIG_SYSCTL */ +static int __init riscv_v_sysctl_init(void) { return 0; } +#endif /* ! CONFIG_SYSCTL */ + +static int riscv_v_init(void) +{ + return riscv_v_sysctl_init(); +} +core_initcall(riscv_v_init); -- 2.17.1
