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From: Arnd Bergmann <arnd@arndb.de>
To: Russell King <linux@armlinux.org.uk>, Christoph Hellwig <hch@lst.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org,
	linux-mm@kvack.org, Arnd Bergmann <arnd@arndb.de>
Subject: [PATCH v3 01/10] mm/maccess: fix unaligned copy_{from,to}_kernel_nofault
Date: Thu,  1 Oct 2020 16:12:24 +0200	[thread overview]
Message-ID: <20201001141233.119343-2-arnd@arndb.de> (raw)
In-Reply-To: <20201001141233.119343-1-arnd@arndb.de>

On machines such as ARMv5 that trap unaligned accesses, these
two functions can be slow when each access needs to be emulated,
or they might not work at all.

Change them so that each loop is only used when both the src
and dst pointers are naturally aligned.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 mm/maccess.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/mm/maccess.c b/mm/maccess.c
index 3bd70405f2d8..d3f1a1f0b1c1 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -24,13 +24,21 @@ bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
 
 long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
 {
+	unsigned long align = 0;
+
+	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
+		align = (unsigned long)dst | (unsigned long)src;
+
 	if (!copy_from_kernel_nofault_allowed(src, size))
 		return -ERANGE;
 
 	pagefault_disable();
-	copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
-	copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
-	copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
+	if (!(align & 7))
+		copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
+	if (!(align & 3))
+		copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
+	if (!(align & 1))
+		copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
 	copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
 	pagefault_enable();
 	return 0;
@@ -50,10 +58,18 @@ EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
 
 long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
 {
+	unsigned long align = 0;
+
+	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
+		align = (unsigned long)dst | (unsigned long)src;
+
 	pagefault_disable();
-	copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
-	copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
-	copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
+	if (!(align & 7))
+		copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
+	if (!(align & 3))
+		copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
+	if (!(align & 1))
+		copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
 	copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
 	pagefault_enable();
 	return 0;
-- 
2.27.0


  reply	other threads:[~2020-10-01 14:13 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-01 14:12 [PATCH v3 00/10] ARM: remove set_fs callers and implementation Arnd Bergmann
2020-10-01 14:12 ` Arnd Bergmann [this message]
2020-10-01 14:12 ` [PATCH v3 02/10] ARM: traps: use get_kernel_nofault instead of set_fs() Arnd Bergmann
2020-10-01 14:12 ` [PATCH v3 03/10] ARM: oabi-compat: add epoll_pwait handler Arnd Bergmann
2020-10-01 14:12 ` [PATCH v3 04/10] ARM: syscall: always store thread_info->syscall Arnd Bergmann
2020-10-01 14:12 ` [PATCH v3 05/10] ARM: oabi-compat: rework epoll_wait/epoll_pwait emulation Arnd Bergmann
2020-10-01 14:12 ` [PATCH v3 06/10] ARM: oabi-compat: rework sys_semtimedop emulation Arnd Bergmann
2020-10-01 14:12 ` [PATCH v3 07/10] ARM: oabi-compat: rework fcntl64() emulation Arnd Bergmann
2020-10-01 14:12 ` [PATCH v3 08/10] ARM: uaccess: add __{get,put}_kernel_nofault Arnd Bergmann
2020-10-01 14:12 ` [PATCH v3 09/10] ARM: provide a TASK_SIZE_MAX definition Arnd Bergmann
2020-10-01 14:12 ` [PATCH v3 10/10] ARM: uaccess: remove set_fs() implementation Arnd Bergmann

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