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Subject[PATCH] [v3] page flags: prioritize kasan bits over last-cpuid
Date
ARM64 randdconfig builds regularly run into a build error, especially
when NUMA_BALANCING and SPARSEMEM are enabled but not SPARSEMEM_VMEMMAP:

#error "KASAN: not enough bits in page flags for tag"

The last-cpuid bits are already contitional on the available space,
so the result of the calculation is a bit random on whether they
were already left out or not.

Adding the kasan tag bits before last-cpuid makes it much more likely
to end up with a successful build here, and should be reliable for
randconfig at least, as long as that does not randomize NR_CPUS
or NODES_SHIFT but uses the defaults.

In order for the modified check to not trigger in the x86 vdso32 code
where all constants are wrong (building with -m32), enclose all the
definitions with an #ifdef.

Fixes: 2813b9c02962 ("kasan, mm, arm64: tag non slab memory allocated via pagealloc")
Link: https://lore.kernel.org/lkml/20190618095347.3850490-1-arnd@arndb.de/
Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v3: rework the #error message to make more sense
v2: fix a build regression with vdso32
---
include/linux/page-flags-layout.h | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/include/linux/page-flags-layout.h b/include/linux/page-flags-layout.h
index 1dda31825ec4..71283739ffd2 100644
--- a/include/linux/page-flags-layout.h
+++ b/include/linux/page-flags-layout.h
@@ -32,6 +32,7 @@

#endif /* CONFIG_SPARSEMEM */

+#ifndef BUILD_VDSO32_64
/*
* page->flags layout:
*
@@ -76,20 +77,22 @@
#define LAST_CPUPID_SHIFT 0
#endif

-#if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT+LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
+#ifdef CONFIG_KASAN_SW_TAGS
+#define KASAN_TAG_WIDTH 8
+#else
+#define KASAN_TAG_WIDTH 0
+#endif
+
+#if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT+LAST_CPUPID_SHIFT+KASAN_TAG_WIDTH \
+ <= BITS_PER_LONG - NR_PAGEFLAGS
#define LAST_CPUPID_WIDTH LAST_CPUPID_SHIFT
#else
#define LAST_CPUPID_WIDTH 0
#endif

-#ifdef CONFIG_KASAN_SW_TAGS
-#define KASAN_TAG_WIDTH 8
#if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH+LAST_CPUPID_WIDTH+KASAN_TAG_WIDTH \
> BITS_PER_LONG - NR_PAGEFLAGS
-#error "KASAN: not enough bits in page flags for tag"
-#endif
-#else
-#define KASAN_TAG_WIDTH 0
+#error "Not enough bits in page flags"
#endif

/*
@@ -104,4 +107,5 @@
#define LAST_CPUPID_NOT_IN_PAGE_FLAGS
#endif

+#endif
#endif /* _LINUX_PAGE_FLAGS_LAYOUT */
--
2.20.0
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