Dave Martin <Dave.Martin@xxxxxxx> writes: > This patch implements the core logic for changing a task's vector > length on request from userspace. This will be used by the ptrace > and prctl frontends that are implemented in later patches. > > The SVE architecture permits, but does not require, implementations > to support vector lengths that are not a power of two. To handle > this, logic is added to check a requested vector length against a > possibly sparse bitmap of available vector lengths at runtime, so > that the best supported value can be chosen. > > Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx> > Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx> > Cc: Alex Bennée <alex.bennee@xxxxxxxxxx> Reviewed-by: Alex Bennée <alex.bennee@xxxxxxxxxx> > --- > arch/arm64/include/asm/fpsimd.h | 8 +++ > arch/arm64/kernel/fpsimd.c | 137 +++++++++++++++++++++++++++++++++++++++- > include/uapi/linux/prctl.h | 5 ++ > 3 files changed, 149 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h > index 9bbd74c..86f550c 100644 > --- a/arch/arm64/include/asm/fpsimd.h > +++ b/arch/arm64/include/asm/fpsimd.h > @@ -20,6 +20,7 @@ > > #ifndef __ASSEMBLY__ > > +#include <linux/cache.h> > #include <linux/stddef.h> > > /* > @@ -70,17 +71,24 @@ extern void fpsimd_update_current_state(struct fpsimd_state *state); > > extern void fpsimd_flush_task_state(struct task_struct *target); > > +/* Maximum VL that SVE VL-agnostic software can transparently support */ > +#define SVE_VL_ARCH_MAX 0x100 > + > extern void sve_save_state(void *state, u32 *pfpsr); > extern void sve_load_state(void const *state, u32 const *pfpsr, > unsigned long vq_minus_1); > extern unsigned int sve_get_vl(void); > > +extern int __ro_after_init sve_max_vl; > + > #ifdef CONFIG_ARM64_SVE > > extern size_t sve_state_size(struct task_struct const *task); > > extern void sve_alloc(struct task_struct *task); > extern void fpsimd_release_task(struct task_struct *task); > +extern int sve_set_vector_length(struct task_struct *task, > + unsigned long vl, unsigned long flags); > > #else /* ! CONFIG_ARM64_SVE */ > > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c > index e0b5ef5..1ceb069 100644 > --- a/arch/arm64/kernel/fpsimd.c > +++ b/arch/arm64/kernel/fpsimd.c > @@ -17,8 +17,10 @@ > * along with this program. If not, see <http://www.gnu.org/licenses/>. > */ > > +#include <linux/bitmap.h> > #include <linux/bottom_half.h> > #include <linux/bug.h> > +#include <linux/cache.h> > #include <linux/compat.h> > #include <linux/cpu.h> > #include <linux/cpu_pm.h> > @@ -28,6 +30,7 @@ > #include <linux/init.h> > #include <linux/percpu.h> > #include <linux/preempt.h> > +#include <linux/prctl.h> > #include <linux/ptrace.h> > #include <linux/sched/signal.h> > #include <linux/signal.h> > @@ -113,6 +116,20 @@ static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state); > /* Default VL for tasks that don't set it explicitly: */ > static int sve_default_vl = SVE_VL_MIN; > > +#ifdef CONFIG_ARM64_SVE > + > +/* Maximum supported vector length across all CPUs (initially poisoned) */ > +int __ro_after_init sve_max_vl = -1; > +/* Set of available vector lengths, as vq_to_bit(vq): */ > +static DECLARE_BITMAP(sve_vq_map, SVE_VQ_MAX); > + > +#else /* ! CONFIG_ARM64_SVE */ > + > +/* Dummy declaration for code that will be optimised out: */ > +extern DECLARE_BITMAP(sve_vq_map, SVE_VQ_MAX); > + > +#endif /* ! CONFIG_ARM64_SVE */ > + > /* > * Call __sve_free() directly only if you know task can't be scheduled > * or preempted. > @@ -270,6 +287,50 @@ static void task_fpsimd_save(void) > } > } > > +/* > + * Helpers to translate bit indices in sve_vq_map to VQ values (and > + * vice versa). This allows find_next_bit() to be used to find the > + * _maximum_ VQ not exceeding a certain value. > + */ > + > +static unsigned int vq_to_bit(unsigned int vq) > +{ > + return SVE_VQ_MAX - vq; > +} > + > +static unsigned int bit_to_vq(unsigned int bit) > +{ > + if (WARN_ON(bit >= SVE_VQ_MAX)) > + bit = SVE_VQ_MAX - 1; > + > + return SVE_VQ_MAX - bit; > +} > + > +/* > + * All vector length selection from userspace comes through here. > + * We're on a slow path, so some sanity-checks are included. > + * If things go wrong there's a bug somewhere, but try to fall back to a > + * safe choice. > + */ > +static unsigned int find_supported_vector_length(unsigned int vl) > +{ > + int bit; > + int max_vl = sve_max_vl; > + > + if (WARN_ON(!sve_vl_valid(vl))) > + vl = SVE_VL_MIN; > + > + if (WARN_ON(!sve_vl_valid(max_vl))) > + max_vl = SVE_VL_MIN; > + > + if (vl > max_vl) > + vl = max_vl; > + > + bit = find_next_bit(sve_vq_map, SVE_VQ_MAX, > + vq_to_bit(sve_vq_from_vl(vl))); > + return sve_vl_from_vq(bit_to_vq(bit)); > +} > + > #define ZREG(sve_state, vq, n) ((char *)(sve_state) + \ > (SVE_SIG_ZREG_OFFSET(vq, n) - SVE_SIG_REGS_OFFSET)) > > @@ -364,6 +425,76 @@ void sve_alloc(struct task_struct *task) > BUG_ON(!task->thread.sve_state); > } > > +int sve_set_vector_length(struct task_struct *task, > + unsigned long vl, unsigned long flags) > +{ > + if (flags & ~(unsigned long)(PR_SVE_VL_INHERIT | > + PR_SVE_SET_VL_ONEXEC)) > + return -EINVAL; > + > + if (!sve_vl_valid(vl)) > + return -EINVAL; > + > + /* > + * Clamp to the maximum vector length that VL-agnostic SVE code can > + * work with. A flag may be assigned in the future to allow setting > + * of larger vector lengths without confusing older software. > + */ > + if (vl > SVE_VL_ARCH_MAX) > + vl = SVE_VL_ARCH_MAX; > + > + vl = find_supported_vector_length(vl); > + > + if (flags & (PR_SVE_VL_INHERIT | > + PR_SVE_SET_VL_ONEXEC)) > + task->thread.sve_vl_onexec = vl; > + else > + /* Reset VL to system default on next exec: */ > + task->thread.sve_vl_onexec = 0; > + > + /* Only actually set the VL if not deferred: */ > + if (flags & PR_SVE_SET_VL_ONEXEC) > + goto out; > + > + if (vl == task->thread.sve_vl) > + goto out; > + > + /* > + * To ensure the FPSIMD bits of the SVE vector registers are preserved, > + * write any live register state back to task_struct, and convert to a > + * non-SVE thread. > + */ > + if (task == current) { > + local_bh_disable(); > + > + task_fpsimd_save(); > + set_thread_flag(TIF_FOREIGN_FPSTATE); > + } > + > + fpsimd_flush_task_state(task); > + if (test_and_clear_tsk_thread_flag(task, TIF_SVE)) > + sve_to_fpsimd(task); > + > + if (task == current) > + local_bh_enable(); > + > + /* > + * Force reallocation of task SVE state to the correct size > + * on next use: > + */ > + sve_free(task); > + > + task->thread.sve_vl = vl; > + > +out: > + if (flags & PR_SVE_VL_INHERIT) > + set_tsk_thread_flag(task, TIF_SVE_VL_INHERIT); > + else > + clear_tsk_thread_flag(task, TIF_SVE_VL_INHERIT); > + > + return 0; > +} > + > /* > * Called from the put_task_struct() path, which cannot get here > * unless dead_task is really dead and not schedulable. > @@ -480,7 +611,7 @@ void fpsimd_thread_switch(struct task_struct *next) > > void fpsimd_flush_thread(void) > { > - int vl; > + int vl, supported_vl; > > if (!system_supports_fpsimd()) > return; > @@ -508,6 +639,10 @@ void fpsimd_flush_thread(void) > if (WARN_ON(!sve_vl_valid(vl))) > vl = SVE_VL_MIN; > > + supported_vl = find_supported_vector_length(vl); > + if (WARN_ON(supported_vl != vl)) > + vl = supported_vl; > + > current->thread.sve_vl = vl; > > /* > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h > index a8d0759..1b64901 100644 > --- a/include/uapi/linux/prctl.h > +++ b/include/uapi/linux/prctl.h > @@ -197,4 +197,9 @@ struct prctl_mm_map { > # define PR_CAP_AMBIENT_LOWER 3 > # define PR_CAP_AMBIENT_CLEAR_ALL 4 > > +/* arm64 Scalable Vector Extension controls */ > +# define PR_SVE_SET_VL_ONEXEC (1 << 18) /* defer effect until exec */ > +# define PR_SVE_VL_LEN_MASK 0xffff > +# define PR_SVE_VL_INHERIT (1 << 17) /* inherit across exec */ > + > #endif /* _LINUX_PRCTL_H */ -- Alex Bennée
