6.8-stable patches

added patches:
	arm64-fpsimd-avoid-erroneous-elide-of-user-state-reload.patch
	series

diff --git a/queue-6.8/arm64-fpsimd-avoid-erroneous-elide-of-user-state-reload.patch b/queue-6.8/arm64-fpsimd-avoid-erroneous-elide-of-user-state-reload.patch
new file mode 100644 (file)
index 0000000..7a63eba
--- /dev/null
+++ b/queue-6.8/arm64-fpsimd-avoid-erroneous-elide-of-user-state-reload.patch
@@ -0,0 +1,123 @@
+From e92bee9f861b466c676f0200be3e46af7bc4ac6b Mon Sep 17 00:00:00 2001
+From: Ard Biesheuvel <ardb@kernel.org>
+Date: Wed, 22 May 2024 11:13:36 +0200
+Subject: arm64/fpsimd: Avoid erroneous elide of user state reload
+
+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
+@@ -1518,6 +1518,27 @@ static void fpsimd_save_kernel_state(str
+       task->thread.kernel_fpsimd_cpu = smp_processor_id();
+ }
+ 
++/*
++ * 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;
+@@ -1535,7 +1556,7 @@ 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
+@@ -1825,27 +1846,6 @@ 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.
+  */

diff --git a/queue-6.8/series b/queue-6.8/series
new file mode 100644 (file)
index 0000000..71bf044
--- /dev/null
+++ b/queue-6.8/series
@@ -0,0 +1 @@
+arm64-fpsimd-avoid-erroneous-elide-of-user-state-reload.patch