[PATCH v6 1/5] x86/asm: Carve out a generic movdir64b() helper for general usage

Dave Jiang
2020-09-24T18:01:14Z

The MOVDIR64B instruction can be used by other wrapper instructions. Move
the asm code to special_insns.h and have iosubmit_cmds512() call the
asm function.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
---
arch/x86/include/asm/io.h | 17 +++--------------
arch/x86/include/asm/special_insns.h | 22 ++++++++++++++++++++++
2 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index e1aa17a468a8..d726459d08e5 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -401,7 +401,7 @@ extern bool phys_mem_access_encrypted(unsigned long phys_addr,

/**
* iosubmit_cmds512 - copy data to single MMIO location, in 512-bit units
- * @__dst: destination, in MMIO space (must be 512-bit aligned)
+ * @dst: destination, in MMIO space (must be 512-bit aligned)
* @src: source
* @count: number of 512 bits quantities to submit
*
@@ -412,25 +412,14 @@ extern bool phys_mem_access_encrypted(unsigned long phys_addr,
* Warning: Do not use this helper unless your driver has checked that the CPU
* instruction is supported on the platform.
*/
-static inline void iosubmit_cmds512(void __iomem *__dst, const void *src,
+static inline void iosubmit_cmds512(void __iomem *dst, const void *src,
size_t count)
{
- /*
- * Note that this isn't an "on-stack copy", just definition of "dst"
- * as a pointer to 64-bytes of stuff that is going to be overwritten.
- * In the MOVDIR64B case that may be needed as you can use the
- * MOVDIR64B instruction to copy arbitrary memory around. This trick
- * lets the compiler know how much gets clobbered.
- */
- volatile struct { char _[64]; } *dst = __dst;
const u8 *from = src;
const u8 *end = from + count * 64;

while (from < end) {
- /* MOVDIR64B [rdx], rax */
- asm volatile(".byte 0x66, 0x0f, 0x38, 0xf8, 0x02"
- : "=m" (dst)
- : "d" (from), "a" (dst));
+ movdir64b(dst, from);
from += 64;
}
}
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 59a3e13204c3..2258c7d6e281 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -234,6 +234,28 @@ static inline void clwb(volatile void *__p)

#define nop() asm volatile ("nop")

+/* The dst parameter must be 64-bytes aligned */
+static inline void movdir64b(void *dst, const void *src)
+{
+ const struct { char _[64]; } *__src = src;
+ struct { char _[64]; } *__dst = dst;
+
+ /*
+ * MOVDIR64B %(rdx), rax.
+ *
+ * Both __src and __dst must be memory constraints in order to tell the
+ * compiler that no other memory accesses should be reordered around
+ * this one.
+ *
+ * Also, both must be supplied as lvalues because this tells
+ * the compiler what the object is (its size) the instruction accesses.
+ * I.e., not the pointers but what they point, thus the deref'ing '*'.
+ */
+ asm volatile(".byte 0x66, 0x0f, 0x38, 0xf8, 0x02"
+ : "+m" (*__dst)
+ : "m" (*__src), "a" (__dst), "d" (__src));
+}
+
#endif /* __KERNEL__ */

#endif /* _ASM_X86_SPECIAL_INSNS_H */
--
2.21.3