6.8-stable review patch. If anyone has any objections, please let me know.
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From: Ard Biesheuvel ardb@kernel.org
commit e92bee9f861b466c676f0200be3e46af7bc4ac6b upstream.
TIF_FOREIGN_FPSTATE is a 'convenience' flag that should reflect whether the current CPU holds the most recent user mode FP/SIMD state of the current task. It combines two conditions: - whether the current CPU's FP/SIMD state belongs to the task; - whether that state is the most recent associated with the task (as a task may have executed on other CPUs as well).
When a task is scheduled in and TIF_KERNEL_FPSTATE is set, it means the task was in a kernel mode NEON section when it was scheduled out, and so the kernel mode FP/SIMD state is restored. Since this implies that the current CPU is *not* holding the most recent user mode FP/SIMD state of the current task, the TIF_FOREIGN_FPSTATE flag is set too, so that the user mode FP/SIMD state is reloaded from memory when returning to userland.
However, the task may be scheduled out after completing the kernel mode NEON section, but before returning to userland. When this happens, the TIF_FOREIGN_FPSTATE flag will not be preserved, but will be set as usual the next time the task is scheduled in, and will be based on the above conditions.
This means that, rather than setting TIF_FOREIGN_FPSTATE when scheduling in a task with TIF_KERNEL_FPSTATE set, the underlying state should be updated so that TIF_FOREIGN_FPSTATE will assume the expected value as a result.
So instead, call fpsimd_flush_cpu_state(), which takes care of this.
Closes: https://lore.kernel.org/all/cb8822182231850108fa43e0446a4c7f@kernel.org Reported-by: Johannes Nixdorf mixi@shadowice.org Fixes: aefbab8e77eb ("arm64: fpsimd: Preserve/restore kernel mode NEON at context switch") Cc: Mark Brown broonie@kernel.org Cc: Dave Martin Dave.Martin@arm.com Cc: Janne Grunau j@jannau.net Cc: stable@vger.kernel.org Signed-off-by: Ard Biesheuvel ardb@kernel.org Tested-by: Janne Grunau j@jannau.net Tested-by: Johannes Nixdorf mixi@shadowice.org Reviewed-by: Mark Brown broonie@kernel.org Link: https://lore.kernel.org/r/20240522091335.335346-2-ardb+git@google.com Signed-off-by: Will Deacon will@kernel.org Cc: Florian Klink flokli@flokli.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/kernel/fpsimd.c | 44 ++++++++++++++++++++++---------------------- 1 file changed, 22 insertions(+), 22 deletions(-)
--- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -1500,6 +1500,27 @@ static void fpsimd_save_kernel_state(str fpsimd_save_state(&task->thread.kernel_fpsimd_state); }
+/* + * Invalidate any task's FPSIMD state that is present on this cpu. + * The FPSIMD context should be acquired with get_cpu_fpsimd_context() + * before calling this function. + */ +static void fpsimd_flush_cpu_state(void) +{ + WARN_ON(!system_supports_fpsimd()); + __this_cpu_write(fpsimd_last_state.st, NULL); + + /* + * Leaving streaming mode enabled will cause issues for any kernel + * NEON and leaving streaming mode or ZA enabled may increase power + * consumption. + */ + if (system_supports_sme()) + sme_smstop(); + + set_thread_flag(TIF_FOREIGN_FPSTATE); +} + void fpsimd_thread_switch(struct task_struct *next) { bool wrong_task, wrong_cpu; @@ -1517,7 +1538,7 @@ void fpsimd_thread_switch(struct task_st
if (test_tsk_thread_flag(next, TIF_KERNEL_FPSTATE)) { fpsimd_load_kernel_state(next); - set_tsk_thread_flag(next, TIF_FOREIGN_FPSTATE); + fpsimd_flush_cpu_state(); } else { /* * Fix up TIF_FOREIGN_FPSTATE to correctly describe next's @@ -1807,27 +1828,6 @@ void fpsimd_flush_task_state(struct task }
/* - * Invalidate any task's FPSIMD state that is present on this cpu. - * The FPSIMD context should be acquired with get_cpu_fpsimd_context() - * before calling this function. - */ -static void fpsimd_flush_cpu_state(void) -{ - WARN_ON(!system_supports_fpsimd()); - __this_cpu_write(fpsimd_last_state.st, NULL); - - /* - * Leaving streaming mode enabled will cause issues for any kernel - * NEON and leaving streaming mode or ZA enabled may increase power - * consumption. - */ - if (system_supports_sme()) - sme_smstop(); - - set_thread_flag(TIF_FOREIGN_FPSTATE); -} - -/* * Save the FPSIMD state to memory and invalidate cpu view. * This function must be called with preemption disabled. */