linux-kernel - Re: [PATCH v7 3/3] x86, mce: Add __mcsafe

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Date:	Wed, 6 Jan 2016 07:06:41 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	"Williams, Dan J" <dan.j.williams@...el.com>
CC:	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	"Elliott, Robert (Persistent Memory)" <elliott@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>,
	linux-nvdimm <linux-nvdimm@...1.01.org>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH v7 3/3] x86, mce: Add __mcsafe_copy()

You were heading towards:

ld: undefined __mcsafe_copy

since that is also inside the #ifdef. 

Weren't you going to "select" this?

I'm seriously wondering whether the ifdef still makes sense. Now I don't have an extra exception table and routines to sort/search/fixup, it doesn't seem as useful as it was a few iterations ago.

Sent from my iPhone

> On Jan 5, 2016, at 20:43, Dan Williams <dan.j.williams@...el.com> wrote:
> 
>> On Thu, Dec 31, 2015 at 11:43 AM, Tony Luck <tony.luck@...el.com> wrote:
>> Make use of the EXTABLE_FAULT exception table entries. This routine
>> returns a structure to indicate the result of the copy:
>> 
>> struct mcsafe_ret {
>>        u64 trapnr;
>>        u64 remain;
>> };
>> 
>> If the copy is successful, then both 'trapnr' and 'remain' are zero.
>> 
>> If we faulted during the copy, then 'trapnr' will say which type
>> of trap (X86_TRAP_PF or X86_TRAP_MC) and 'remain' says how many
>> bytes were not copied.
>> 
>> Signed-off-by: Tony Luck <tony.luck@...el.com>
>> ---
>> arch/x86/Kconfig                 |  10 +++
>> arch/x86/include/asm/string_64.h |  10 +++
>> arch/x86/kernel/x8664_ksyms_64.c |   4 ++
>> arch/x86/lib/memcpy_64.S         | 136 +++++++++++++++++++++++++++++++++++++++
>> 4 files changed, 160 insertions(+)
>> 
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 96d058a87100..42d26b4d1ec4 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -1001,6 +1001,16 @@ config X86_MCE_INJECT
>>          If you don't know what a machine check is and you don't do kernel
>>          QA it is safe to say n.
>> 
>> +config MCE_KERNEL_RECOVERY
>> +       bool "Recovery from machine checks in special kernel memory copy functions"
>> +       default n
>> +       depends on X86_MCE && X86_64
>> +       ---help---
>> +         This option provides a new memory copy function mcsafe_memcpy()
>> +         that is annotated to allow the machine check handler to return
>> +         to an alternate code path to return an error to the caller instead
>> +         of crashing the system. Say yes if you have a driver that uses this.
>> +
>> config X86_THERMAL_VECTOR
>>        def_bool y
>>        depends on X86_MCE_INTEL
>> diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
>> index ff8b9a17dc4b..16a8f0e56e4a 100644
>> --- a/arch/x86/include/asm/string_64.h
>> +++ b/arch/x86/include/asm/string_64.h
>> @@ -78,6 +78,16 @@ int strcmp(const char *cs, const char *ct);
>> #define memset(s, c, n) __memset(s, c, n)
>> #endif
>> 
>> +#ifdef CONFIG_MCE_KERNEL_RECOVERY
>> +struct mcsafe_ret {
>> +       u64 trapnr;
>> +       u64 remain;
>> +};
> 
> Can we move this definition outside of the CONFIG_MCE_KERNEL_RECOVERY
> ifdef guard?  On a test integration branch the kbuild robot caught the
> following:
> 
>   In file included from include/linux/pmem.h:21:0,
>                    from drivers/acpi/nfit.c:22:
>   arch/x86/include/asm/pmem.h: In function 'arch_memcpy_from_pmem':
>>> arch/x86/include/asm/pmem.h:55:21: error: storage size of 'ret' isn't known
>      struct mcsafe_ret ret;
>                        ^
>>> arch/x86/include/asm/pmem.h:57:9: error: implicit declaration of function '__mcsafe_copy' [-Werror=implicit-function-declaration]
>      ret = __mcsafe_copy(dst, (void __force *) src, n);
>            ^
>>> arch/x86/include/asm/pmem.h:55:21: warning: unused variable 'ret' [-Wunused-variable]
>      struct mcsafe_ret ret;
>                        ^
>   cc1: some warnings being treated as errors
> 
> vim +55 arch/x86/include/asm/pmem.h
> 
>    49  }
>    50
>    51  static inline int arch_memcpy_from_pmem(void *dst, const void
> __pmem *src,
>    52                  size_t n)
>    53  {
>    54          if (IS_ENABLED(CONFIG_MCE_KERNEL_RECOVERY)) {
>> 55                  struct mcsafe_ret ret;
>    56
>> 57                  ret = __mcsafe_copy(dst, (void __force *) src, n);
>    58                  if (ret.remain)
>    59                          return -EIO;
>    60                  return 0;
--
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