[tip: core/mm] asm-generic: Provide kmap_size.h

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the core/mm branch of tip:

Commit-ID:     4f8b96cd47b06f1e3ec71c1a3216113efe8dbfb5
Gitweb:        https://git.kernel.org/tip/4f8b96cd47b06f1e3ec71c1a3216113efe8dbfb5
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Tue, 03 Nov 2020 10:27:17 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Fri, 06 Nov 2020 23:14:54 +01:00

asm-generic: Provide kmap_size.h

kmap_types.h is a misnomer because the old atomic MAP based array does not
exist anymore and the whole indirection of architectures including
kmap_types.h is inconinstent and does not allow to provide guard page
debugging for this misfeature.

Add a common header file which defines the mapping stack size for all
architectures. Will be used when converting architectures over to a
generic kmap_local/atomic implementation.

The array size is chosen with the following constraints in mind:

    - The deepest nest level in one context is 3 according to code
      inspection.

    - The worst case nesting for the upcoming reemptible version would be:

      2 maps in task context and a fault inside
      2 maps in the fault handler
      3 maps in softirq
      2 maps in interrupt

So a total of 16 is sufficient and probably overestimated.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20201103095857.078043987@xxxxxxxxxxxxx

---
 include/asm-generic/Kbuild      |  1 +
 include/asm-generic/kmap_size.h | 12 ++++++++++++
 2 files changed, 13 insertions(+)
 create mode 100644 include/asm-generic/kmap_size.h

diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
index e78bbb9..ed62d38 100644
--- a/include/asm-generic/Kbuild
+++ b/include/asm-generic/Kbuild
@@ -31,6 +31,7 @@ mandatory-y += irq_regs.h
 mandatory-y += irq_work.h
 mandatory-y += kdebug.h
 mandatory-y += kmap_types.h
+mandatory-y += kmap_size.h
 mandatory-y += kprobes.h
 mandatory-y += linkage.h
 mandatory-y += local.h
diff --git a/include/asm-generic/kmap_size.h b/include/asm-generic/kmap_size.h
new file mode 100644
index 0000000..9d6c778
--- /dev/null
+++ b/include/asm-generic/kmap_size.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_KMAP_SIZE_H
+#define _ASM_GENERIC_KMAP_SIZE_H
+
+/* For debug this provides guard pages between the maps */
+#ifdef CONFIG_DEBUG_HIGHMEM
+# define KM_MAX_IDX	33
+#else
+# define KM_MAX_IDX	16
+#endif
+
+#endif