1 files changed, 35 insertions, 0 deletions
diff --git a/debian/patches-rt/arm-Disable-FAST_GUP-on-PREEMPT_RT-if-HIGHPTE-is-als.patch b/debian/patches-rt/arm-Disable-FAST_GUP-on-PREEMPT_RT-if-HIGHPTE-is-als.patch
new file mode 100644
index 000000000..09dcd78d5
--- /dev/null
+++ b/debian/patches-rt/arm-Disable-FAST_GUP-on-PREEMPT_RT-if-HIGHPTE-is-als.patch
@@ -0,0 +1,35 @@
+From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Date: Tue, 23 Jan 2024 12:56:21 +0100
+Subject: [PATCH] arm: Disable FAST_GUP on PREEMPT_RT if HIGHPTE is also
+ enabled.
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.8/older/patches-6.8.2-rt11.tar.xz
+
+gup_pgd_range() is invoked with disabled interrupts and invokes
+__kmap_local_page_prot() via pte_offset_map(), gup_p4d_range().
+With HIGHPTE enabled, __kmap_local_page_prot() invokes kmap_high_get()
+which uses a spinlock_t via lock_kmap_any(). This leads to an
+sleeping-while-atomic error on PREEMPT_RT because spinlock_t becomes a
+sleeping lock and must not be acquired in atomic context.
+
+The loop in map_new_virtual() uses wait_queue_head_t for wake up which
+also is using a spinlock_t.
+
+Limit HAVE_FAST_GUP additionaly to remain disabled on PREEMPT_RT with
+HIGHPTE enabled.
+
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ arch/arm/Kconfig |    2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+--- a/arch/arm/Kconfig
++++ b/arch/arm/Kconfig
+@@ -98,7 +98,7 @@ config ARM
+ 	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
+ 	select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU
+ 	select HAVE_EXIT_THREAD
+-	select HAVE_FAST_GUP if ARM_LPAE
++	select HAVE_FAST_GUP if ARM_LPAE && !(PREEMPT_RT && HIGHPTE)
+ 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
+ 	select HAVE_FUNCTION_ERROR_INJECTION
+ 	select HAVE_FUNCTION_GRAPH_TRACER