linux-kernel - [PATCH V2] LoongArch: Remove shm_align

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Date:   Tue, 29 Aug 2023 10:58:41 +0800
From:   Huacai Chen <chenhuacai@...ngson.cn>
To:     Arnd Bergmann <arnd@...db.de>, Huacai Chen <chenhuacai@...nel.org>
Cc:     loongarch@...ts.linux.dev, linux-arch@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Guo Ren <guoren@...nel.org>, Xuerui Wang <kernel@...0n.name>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn,
        Huacai Chen <chenhuacai@...ngson.cn>,
        Jiantao Shan <shanjiantao@...ngson.cn>
Subject: [PATCH V2] LoongArch: Remove shm_align_mask and use SHMLBA instead

Both shm_align_mask and SHMLBA want to avoid cache alias. But they are
inconsistent: shm_align_mask is (PAGE_SIZE - 1) while SHMLBA is SZ_64K,
but PAGE_SIZE is not always equal to SZ_64K.

This may cause problems when shmat() twice. Fix this problem by removing
shm_align_mask and using SHMLBA (strictly SHMLBA - 1) instead.

Reported-by: Jiantao Shan <shanjiantao@...ngson.cn>
Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
---
V2: Define SHM_ALIGN_MASK.

 arch/loongarch/mm/cache.c |  1 -
 arch/loongarch/mm/mmap.c  | 13 ++++++-------
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/arch/loongarch/mm/cache.c b/arch/loongarch/mm/cache.c
index 72685a48eaf0..6be04d36ca07 100644
--- a/arch/loongarch/mm/cache.c
+++ b/arch/loongarch/mm/cache.c
@@ -156,7 +156,6 @@ void cpu_cache_init(void)
 
 	current_cpu_data.cache_leaves_present = leaf;
 	current_cpu_data.options |= LOONGARCH_CPU_PREFETCH;
-	shm_align_mask = PAGE_SIZE - 1;
 }
 
 static const pgprot_t protection_map[16] = {
diff --git a/arch/loongarch/mm/mmap.c b/arch/loongarch/mm/mmap.c
index fbe1a4856fc4..a9630a81b38a 100644
--- a/arch/loongarch/mm/mmap.c
+++ b/arch/loongarch/mm/mmap.c
@@ -8,12 +8,11 @@
 #include <linux/mm.h>
 #include <linux/mman.h>
 
-unsigned long shm_align_mask = PAGE_SIZE - 1;	/* Sane caches */
-EXPORT_SYMBOL(shm_align_mask);
+#define SHM_ALIGN_MASK	(SHMLBA - 1)
 
-#define COLOUR_ALIGN(addr, pgoff)				\
-	((((addr) + shm_align_mask) & ~shm_align_mask) +	\
-	 (((pgoff) << PAGE_SHIFT) & shm_align_mask))
+#define COLOUR_ALIGN(addr, pgoff)			\
+	((((addr) + SHM_ALIGN_MASK) & ~SHM_ALIGN_MASK)	\
+	 + (((pgoff) << PAGE_SHIFT) & SHM_ALIGN_MASK))
 
 enum mmap_allocation_direction {UP, DOWN};
 
@@ -40,7 +39,7 @@ static unsigned long arch_get_unmapped_area_common(struct file *filp,
 		 * cache aliasing constraints.
 		 */
 		if ((flags & MAP_SHARED) &&
-		    ((addr - (pgoff << PAGE_SHIFT)) & shm_align_mask))
+		    ((addr - (pgoff << PAGE_SHIFT)) & SHM_ALIGN_MASK))
 			return -EINVAL;
 		return addr;
 	}
@@ -63,7 +62,7 @@ static unsigned long arch_get_unmapped_area_common(struct file *filp,
 	}
 
 	info.length = len;
-	info.align_mask = do_color_align ? (PAGE_MASK & shm_align_mask) : 0;
+	info.align_mask = do_color_align ? (PAGE_MASK & SHM_ALIGN_MASK) : 0;
 	info.align_offset = pgoff << PAGE_SHIFT;
 
 	if (dir == DOWN) {
-- 
2.39.3