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.Martin@xxxxxxx>
---
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
