linux-kernel - [PATCH v2] mm/ioremap: Fix iomap_max_page

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Date:   Thu, 13 May 2021 09:29:53 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nicholas Piggin <npiggin@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v2] mm/ioremap: Fix iomap_max_page_shift

iomap_max_page_shift is expected to contain a page shift,
so it can't be a 'bool', has to be an 'unsigned int'

And fix the default values: P4D_SHIFT is when huge iomap is allowed.

However, on some architectures (eg: powerpc book3s/64), P4D_SHIFT is
not a constant so it can't be used to initialise a static variable.
So, initialise iomap_max_page_shift with a maximum shift supported
by the architecture, it is gated by P4D_SHIFT in vmap_try_huge_p4d()
anyway.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
Fixes: bbc180a5adb0 ("mm: HUGE_VMAP arch support cleanup")
Reviewed-by: Nicholas Piggin <npiggin@...il.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>
---
v2: Initialise with BITS_PER_LONG - 1 instead of P4D_SHIFT which is not a constant on powerpc/64.
---
 mm/ioremap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/ioremap.c b/mm/ioremap.c
index d1dcc7e744ac..8ee0136f8cb0 100644
--- a/mm/ioremap.c
+++ b/mm/ioremap.c
@@ -16,16 +16,16 @@
 #include "pgalloc-track.h"
 
 #ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
-static bool __ro_after_init iomap_max_page_shift = PAGE_SHIFT;
+static unsigned int __ro_after_init iomap_max_page_shift = BITS_PER_LONG - 1;
 
 static int __init set_nohugeiomap(char *str)
 {
-	iomap_max_page_shift = P4D_SHIFT;
+	iomap_max_page_shift = PAGE_SHIFT;
 	return 0;
 }
 early_param("nohugeiomap", set_nohugeiomap);
 #else /* CONFIG_HAVE_ARCH_HUGE_VMAP */
-static const bool iomap_max_page_shift = PAGE_SHIFT;
+static const unsigned int iomap_max_page_shift = PAGE_SHIFT;
 #endif	/* CONFIG_HAVE_ARCH_HUGE_VMAP */
 
 int ioremap_page_range(unsigned long addr,
-- 
2.25.0