linux-kernel - Re: Question Regarding ERMS memcpy

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Date:   Mon, 06 Mar 2017 05:41:22 -0800
From:   hpa@...or.com
To:     Borislav Petkov <bp@...e.de>,
        Logan Gunthorpe <logang@...tatee.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Tony Luck <tony.luck@...el.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Question Regarding ERMS memcpy

On March 6, 2017 5:33:28 AM PST, Borislav Petkov <bp@...e.de> wrote:
>On Mon, Mar 06, 2017 at 12:01:10AM -0700, Logan Gunthorpe wrote:
>> Well honestly my issue was solved by fixing my kernel config. I have
>no
>> idea why I had optimize for size in there in the first place.
>
>I still think that we should address the iomem memcpy Linus mentioned.
>So how about this partial revert. I've made 32-bit use the same special
>__memcpy() version.
>
>Hmmm?
>
>---
>diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
>index 7afb0e2f07f4..9e378a10796d 100644
>--- a/arch/x86/include/asm/io.h
>+++ b/arch/x86/include/asm/io.h
>@@ -201,6 +201,7 @@ extern void set_iounmap_nonlazy(void);
> #ifdef __KERNEL__
> 
> #include <asm-generic/iomap.h>
>+#include <asm/string.h>
> 
> /*
>  * Convert a virtual cached pointer to an uncached pointer
>@@ -227,12 +228,13 @@ memset_io(volatile void __iomem *addr, unsigned
>char val, size_t count)
>  * @src:		The (I/O memory) source for the data
>  * @count:		The number of bytes to copy
>  *
>- * Copy a block of data from I/O memory.
>+ * Copy a block of data from I/O memory. IO memory is different from
>+ * cached memory so we use special memcpy version.
>  */
> static inline void
>memcpy_fromio(void *dst, const volatile void __iomem *src, size_t
>count)
> {
>-	memcpy(dst, (const void __force *)src, count);
>+	__inline_memcpy(dst, (const void __force *)src, count);
> }
> 
> /**
>@@ -241,12 +243,13 @@ memcpy_fromio(void *dst, const volatile void
>__iomem *src, size_t count)
>  * @src:		The (RAM) source for the data
>  * @count:		The number of bytes to copy
>  *
>- * Copy a block of data to I/O memory.
>+ * Copy a block of data to I/O memory. IO memory is different from
>+ * cached memory so we use special memcpy version.
>  */
> static inline void
> memcpy_toio(volatile void __iomem *dst, const void *src, size_t count)
> {
>-	memcpy((void __force *)dst, src, count);
>+	__inline_memcpy((void __force *)dst, src, count);
> }
> 
> /*
>diff --git a/arch/x86/include/asm/string_32.h
>b/arch/x86/include/asm/string_32.h
>index 3d3e8353ee5c..556fa4a975ff 100644
>--- a/arch/x86/include/asm/string_32.h
>+++ b/arch/x86/include/asm/string_32.h
>@@ -29,6 +29,7 @@ extern char *strchr(const char *s, int c);
> #define __HAVE_ARCH_STRLEN
> extern size_t strlen(const char *s);
> 
>+#define __inline_memcpy __memcpy
>static __always_inline void *__memcpy(void *to, const void *from,
>size_t n)
> {
> 	int d0, d1, d2;

It isn't really that straightforward IMO.

For UC memory transaction size really needs to be specified explicitly at all times and should be part of the API, rather than implicit.

For WC/WT/WB device memory, the ordinary memcpy is valid and preferred.
-- 
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