[PATCH 4.4 12/34] lib/mpi: Fix umul_ppmm() for MIPS64r6

[PATCH 4.4 12/34] lib/mpi: Fix umul_ppmm() for MIPS64r6

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: James Hogan <jhogan@kernel.org>


[ Upstream commit bbc25bee37d2b32cf3a1fab9195b6da3a185614a ]

Current MIPS64r6 toolchains aren't able to generate efficient
DMULU/DMUHU based code for the C implementation of umul_ppmm(), which
performs an unsigned 64 x 64 bit multiply and returns the upper and
lower 64-bit halves of the 128-bit result. Instead it widens the 64-bit
inputs to 128-bits and emits a __multi3 intrinsic call to perform a 128
x 128 multiply. This is both inefficient, and it results in a link error
since we don't include __multi3 in MIPS linux.

For example commit 90a53e4432b1 ("cfg80211: implement regdb signature
checking") merged in v4.15-rc1 recently broke the 64r6_defconfig and
64r6el_defconfig builds by indirectly selecting MPILIB. The same build
errors can be reproduced on older kernels by enabling e.g. CRYPTO_RSA:

lib/mpi/generic_mpih-mul1.o: In function `mpihelp_mul_1':
lib/mpi/generic_mpih-mul1.c:50: undefined reference to `__multi3'
lib/mpi/generic_mpih-mul2.o: In function `mpihelp_addmul_1':
lib/mpi/generic_mpih-mul2.c:49: undefined reference to `__multi3'
lib/mpi/generic_mpih-mul3.o: In function `mpihelp_submul_1':
lib/mpi/generic_mpih-mul3.c:49: undefined reference to `__multi3'
lib/mpi/mpih-div.o In function `mpihelp_divrem':
lib/mpi/mpih-div.c:205: undefined reference to `__multi3'
lib/mpi/mpih-div.c:142: undefined reference to `__multi3'

Therefore add an efficient MIPS64r6 implementation of umul_ppmm() using
inline assembly and the DMULU/DMUHU instructions, to prevent __multi3
calls being emitted.

Fixes: 7fd08ca58ae6 ("MIPS: Add build support for the MIPS R6 ISA")
Signed-off-by: James Hogan <jhogan@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-mips@linux-mips.org
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 lib/mpi/longlong.h |   18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

--- a/lib/mpi/longlong.h
+++ b/lib/mpi/longlong.h
@@ -671,7 +671,23 @@ do {						\
 	**************  MIPS/64  **************
 	***************************************/
 #if (defined(__mips) && __mips >= 3) && W_TYPE_SIZE == 64
-#if (__GNUC__ >= 5) || (__GNUC__ >= 4 && __GNUC_MINOR__ >= 4)
+#if defined(__mips_isa_rev) && __mips_isa_rev >= 6
+/*
+ * GCC ends up emitting a __multi3 intrinsic call for MIPS64r6 with the plain C
+ * code below, so we special case MIPS64r6 until the compiler can do better.
+ */
+#define umul_ppmm(w1, w0, u, v)						\
+do {									\
+	__asm__ ("dmulu %0,%1,%2"					\
+		 : "=d" ((UDItype)(w0))					\
+		 : "d" ((UDItype)(u)),					\
+		   "d" ((UDItype)(v)));					\
+	__asm__ ("dmuhu %0,%1,%2"					\
+		 : "=d" ((UDItype)(w1))					\
+		 : "d" ((UDItype)(u)),					\
+		   "d" ((UDItype)(v)));					\
+} while (0)
+#elif (__GNUC__ >= 5) || (__GNUC__ >= 4 && __GNUC_MINOR__ >= 4)
 #define umul_ppmm(w1, w0, u, v) \
 do {									\
 	typedef unsigned int __ll_UTItype __attribute__((mode(TI)));	\

[PATCH 4.4 34/34] MIPS: Implement __multi3 for GCC7 MIPS64r6 builds

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: James Hogan <jhogan@kernel.org>

commit ebabcf17bcd7ce968b1631ebe08236275698f39b upstream.

GCC7 is a bit too eager to generate suboptimal __multi3 calls (128bit
multiply with 128bit result) for MIPS64r6 builds, even in code which
doesn't explicitly use 128bit types, such as the following:

unsigned long func(unsigned long a, unsigned long b)
{
	return a > (~0UL) / b;
}

Which GCC rearanges to:

return (unsigned __int128)a * (unsigned __int128)b > 0xffffffffffffffff;

Therefore implement __multi3, but only for MIPS64r6 with GCC7 as under
normal circumstances we wouldn't expect any calls to __multi3 to be
generated from kernel code.

Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: James Hogan <jhogan@kernel.org>
Tested-by: Waldemar Brodkorb <wbx@openadk.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Maciej W. Rozycki <macro@mips.com>
Cc: Matthew Fortune <matthew.fortune@mips.com>
Cc: Florian Fainelli <florian@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17890/
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/mips/lib/Makefile |    3 +-
 arch/mips/lib/libgcc.h |   17 +++++++++++++++
 arch/mips/lib/multi3.c |   54 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 73 insertions(+), 1 deletion(-)

--- a/arch/mips/lib/Makefile
+++ b/arch/mips/lib/Makefile
@@ -15,4 +15,5 @@ obj-$(CONFIG_CPU_R3000)		+= r3k_dump_tlb
 obj-$(CONFIG_CPU_TX39XX)	+= r3k_dump_tlb.o
 
 # libgcc-style stuff needed in the kernel
-obj-y += ashldi3.o ashrdi3.o bswapsi.o bswapdi.o cmpdi2.o lshrdi3.o ucmpdi2.o
+obj-y += ashldi3.o ashrdi3.o bswapsi.o bswapdi.o cmpdi2.o lshrdi3.o multi3.o \
+	 ucmpdi2.o
--- a/arch/mips/lib/libgcc.h
+++ b/arch/mips/lib/libgcc.h
@@ -9,10 +9,18 @@ typedef int word_type __attribute__ ((mo
 struct DWstruct {
 	int high, low;
 };
+
+struct TWstruct {
+	long long high, low;
+};
 #elif defined(__LITTLE_ENDIAN)
 struct DWstruct {
 	int low, high;
 };
+
+struct TWstruct {
+	long long low, high;
+};
 #else
 #error I feel sick.
 #endif
@@ -22,4 +30,13 @@ typedef union {
 	long long ll;
 } DWunion;
 
+#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6)
+typedef int ti_type __attribute__((mode(TI)));
+
+typedef union {
+	struct TWstruct s;
+	ti_type ti;
+} TWunion;
+#endif
+
 #endif /* __ASM_LIBGCC_H */
--- /dev/null
+++ b/arch/mips/lib/multi3.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/export.h>
+
+#include "libgcc.h"
+
+/*
+ * GCC 7 suboptimally generates __multi3 calls for mips64r6, so for that
+ * specific case only we'll implement it here.
+ *
+ * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82981
+ */
+#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ == 7)
+
+/* multiply 64-bit values, low 64-bits returned */
+static inline long long notrace dmulu(long long a, long long b)
+{
+	long long res;
+
+	asm ("dmulu %0,%1,%2" : "=r" (res) : "r" (a), "r" (b));
+	return res;
+}
+
+/* multiply 64-bit unsigned values, high 64-bits of 128-bit result returned */
+static inline long long notrace dmuhu(long long a, long long b)
+{
+	long long res;
+
+	asm ("dmuhu %0,%1,%2" : "=r" (res) : "r" (a), "r" (b));
+	return res;
+}
+
+/* multiply 128-bit values, low 128-bits returned */
+ti_type notrace __multi3(ti_type a, ti_type b)
+{
+	TWunion res, aa, bb;
+
+	aa.ti = a;
+	bb.ti = b;
+
+	/*
+	 * a * b =           (a.lo * b.lo)
+	 *         + 2^64  * (a.hi * b.lo + a.lo * b.hi)
+	 *        [+ 2^128 * (a.hi * b.hi)]
+	 */
+	res.s.low = dmulu(aa.s.low, bb.s.low);
+	res.s.high = dmuhu(aa.s.low, bb.s.low);
+	res.s.high += dmulu(aa.s.high, bb.s.low);
+	res.s.high += dmulu(aa.s.low, bb.s.high);
+
+	return res.ti;
+}
+EXPORT_SYMBOL(__multi3);
+
+#endif /* 64BIT && CPU_MIPSR6 && GCC7 */