[PATCH v2] x86: fix movdir64b() sparse warning

[PATCH v2] x86: fix movdir64b() sparse warning

[Dave Jiang]

Add missing __iomem annotation to address sparse warning. Caller is expected
to pass an __iomem annotated pointer to this function. The current usages
send a 64bytes command descriptor to an MMIO location (portal) on a
device for consumption. When future usages for MOVDIR64B instruction show
up in kernel for memory to memory operation is needed, we can revisit.

Also, from the comment in movdir64b() @__dst must be supplied as an
lvalue because this tells the compiler what the object is (its size)
the instruction accesses. I.e., not the pointers but what they point
to, thus the deref'ing '*'."

"sparse warnings: (new ones prefixed by >>)"
   drivers/dma/idxd/submit.c: note: in included file (through include/linux/io.h, include/linux/pci.h):
>> arch/x86/include/asm/io.h:422:27: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected void *dst @@     got void [noderef] __iomem *dst @@
   arch/x86/include/asm/io.h:422:27: sparse:     expected void *dst
   arch/x86/include/asm/io.h:422:27: sparse:     got void [noderef] __iomem *dst

Fixes: 0888e1030d3e ("x86/asm: Carve out a generic movdir64b() helper for general usage")
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
---

v2:
- Update commit log with comments from Dan.

 arch/x86/include/asm/special_insns.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index cc177b4431ae..4e234645f0c6 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -243,10 +243,10 @@ static inline void serialize(void)
 }
 
 /* The dst parameter must be 64-bytes aligned */
-static inline void movdir64b(void *dst, const void *src)
+static inline void movdir64b(void __iomem *dst, const void *src)
 {
 	const struct { char _[64]; } *__src = src;
-	struct { char _[64]; } *__dst = dst;
+	struct { char _[64]; } __iomem *__dst = dst;
 
 	/*
 	 * MOVDIR64B %(rdx), rax.

Re: [PATCH v2] x86: fix movdir64b() sparse warning

[Borislav Petkov]

On Wed, Jan 06, 2021 at 03:40:25PM -0700, Dave Jiang wrote:

> Subject: Re: [PATCH v2] x86: fix movdir64b() sparse warning

There are a lot of times I don't agree with checkpatch but this time I do:

WARNING: A patch subject line should describe the change not the tool that found it
#2: 
Subject: [PATCH v2] x86: fix movdir64b() sparse warning

Pls fix your other patch subject too.

> Add missing __iomem annotation to address sparse warning. Caller is expected
> to pass an __iomem annotated pointer to this function. The current usages
> send a 64bytes command descriptor to an MMIO location (portal) on a
> device for consumption. When future usages for MOVDIR64B instruction show
> up in kernel for memory to memory operation is needed, we can revisit.

Who's "we"?

-- 
Regards/Gruss,
    Boris.

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