arm64/sve: Support vector length resetting for new processes

It's desirable to be able to reset the vector length to some sane
default for new processes, since the new binary and its libraries
may or may not be SVE-aware.

This patch tracks the desired post-exec vector length (if any) in a
new thread member sve_vl_onexec, and adds a new thread flag
TIF_SVE_VL_INHERIT to control whether to inherit or reset the
vector length.  Currently these are inactive.  Subsequent patches
will provide the capability to configure them.

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>

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index e2f575dbdddd50d94a248b3c10d13a8c1c93493b..c6fddb005dc23d21b69ffe49b4ce12c37c5e3d8a 100644 (file)
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -107,6 +107,7 @@ struct thread_struct {
        struct fpsimd_state     fpsimd_state;
        void                    *sve_state;     /* SVE registers, if any */
        unsigned int            sve_vl;         /* SVE vector length */
+       unsigned int            sve_vl_onexec;  /* SVE vl after next exec */
        unsigned long           fault_address;  /* fault info */
        unsigned long           fault_code;     /* ESR_EL1 value */
        struct debug_info       debug;          /* debugging */

diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 92b7b48576c8771b1a2e5fb9511a01fdb8d2900e..eb431286bacd057b8766ebe2af1b021bd29f2949 100644 (file)
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -95,6 +95,7 @@ void arch_release_task_struct(struct task_struct *tsk);
 #define TIF_SINGLESTEP         21
 #define TIF_32BIT              22      /* 32bit process */
 #define TIF_SVE                        23      /* Scalable Vector Extension in use */
+#define TIF_SVE_VL_INHERIT     24      /* Inherit sve_vl_onexec across exec */
 
 #define _TIF_SIGPENDING                (1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED      (1 << TIF_NEED_RESCHED)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 000b5f9215c6b58f5a2addb9637dd7ddb19fbe53..c7531b85b303e4df7ebb2c596833db4065ff191b 100644 (file)
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -111,6 +111,9 @@
  */
 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;
+
 /*
  * Call __sve_free() directly only if you know task can't be scheduled
  * or preempted.
@@ -474,15 +477,20 @@ void fpsimd_flush_thread(void)
                 * If a bug causes this to go wrong, we make some noise and
                 * try to fudge thread.sve_vl to a safe value here.
                 */
-               vl = current->thread.sve_vl;
-
-               if (vl == 0)
-                       vl = SVE_VL_MIN;
+               vl = current->thread.sve_vl_onexec ?
+                       current->thread.sve_vl_onexec : sve_default_vl;
 
                if (WARN_ON(!sve_vl_valid(vl)))
                        vl = SVE_VL_MIN;
 
                current->thread.sve_vl = vl;
+
+               /*
+                * If the task is not set to inherit, ensure that the vector
+                * length will be reset by a subsequent exec:
+                */
+               if (!test_thread_flag(TIF_SVE_VL_INHERIT))
+                       current->thread.sve_vl_onexec = 0;
        }
 
        set_thread_flag(TIF_FOREIGN_FPSTATE);