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
processes 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.mar...@arm.com>
---
 arch/arm64/include/asm/processor.h   |  1 +
 arch/arm64/include/asm/thread_info.h |  1 +
 arch/arm64/kernel/fpsimd.c           | 13 +++++++++++++
 3 files changed, 15 insertions(+)

diff --git a/arch/arm64/include/asm/processor.h 
b/arch/arm64/include/asm/processor.h
index 969feed..da8802a 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -87,6 +87,7 @@ struct thread_struct {
        struct fpsimd_state     fpsimd_state;
        void                    *sve_state;     /* SVE registers, if any */
        u16                     sve_vl;         /* SVE vector length */
+       u16                     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 1a4b30b..bf9c552 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -97,6 +97,7 @@ struct thread_info {
 #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 37dd1b2..80ecb2d 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -108,6 +108,9 @@ static void task_fpsimd_save(void);
  */
 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 = -1;
+
 static void sve_free(struct task_struct *task)
 {
        kfree(task->thread.sve_state);
@@ -392,6 +395,9 @@ void fpsimd_flush_thread(void)
                clear_thread_flag(TIF_SVE);
                sve_free(current);
 
+               current->thread.sve_vl = current->thread.sve_vl_onexec ?
+                       current->thread.sve_vl_onexec : sve_default_vl;
+
                /*
                 * User tasks must have a valid vector length set, but tasks
                 * forked early (e.g., init) may not initially have one.
@@ -401,6 +407,13 @@ void fpsimd_flush_thread(void)
                 * If not, something went badly wrong.
                 */
                BUG_ON(!sve_vl_valid(current->thread.sve_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);
-- 
2.1.4

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