Re: [PATCH v4 1/5] x86/asm: move the raw asm in iosubmit_cmds512() to special_insns.h

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On 9/23/2020 3:41 AM, Borislav Petkov wrote:
Subject: Re: [PATCH v4 1/5] x86/asm: move the raw asm in iosubmit_cmds512() to special_insns.h

Start patch name with a capital letter: "Move the asm definition.."

Also, calling stuff "raw" and "core" is misleading in the kernel context
- you wanna say simply: "Carve out a generic movdir64b() helper... "

Ok I will update


On Thu, Sep 17, 2020 at 02:15:16PM -0700, Dave Jiang wrote:
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 59a3e13204c3..7bc8e714f37e 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -234,6 +234,23 @@ static inline void clwb(volatile void *__p)
#define nop() asm volatile ("nop") +static inline void movdir64b(void *__dst, const void *src)

Make __dst be the function local variable name and keep "dst", i.e.,
without the underscores, the function parameter name.

Ok will fix


+	/*
+	 * 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;
+
+	/* MOVDIR64B [rdx], rax */
+	asm volatile(".byte 0x66, 0x0f, 0x38, 0xf8, 0x02"
+		     : "=m" (dst)
+		     : "d" (src), "a" (dst));
+}
+
  #endif /* __KERNEL__ */
#endif /* _ASM_X86_SPECIAL_INSNS_H */





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