[PATCH] x86/cpufeature: drop *_MASK_CEHCK

[PATCH] x86/cpufeature: drop *_MASK_CEHCK

[Cao jin]

They are wrappers of BUILD_BUG_ON_ZERO(NCAPINTS != n), which is already
present in corresponding *_MASK_BIT_SET. And fill the missing period in
head comments by the way.

Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
---
 arch/x86/include/asm/cpufeature.h        | 2 --
 arch/x86/include/asm/disabled-features.h | 1 -
 arch/x86/include/asm/required-features.h | 3 +--
 3 files changed, 1 insertion(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 58acda503817..232ffb88039c 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -81,7 +81,6 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
 	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 16, feature_bit) ||	\
 	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 17, feature_bit) ||	\
 	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 18, feature_bit) ||	\
-	   REQUIRED_MASK_CHECK					  ||	\
 	   BUILD_BUG_ON_ZERO(NCAPINTS != 19))
 
 #define DISABLED_MASK_BIT_SET(feature_bit)				\
@@ -104,7 +103,6 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
 	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 16, feature_bit) ||	\
 	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 17, feature_bit) ||	\
 	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 18, feature_bit) ||	\
-	   DISABLED_MASK_CHECK					  ||	\
 	   BUILD_BUG_ON_ZERO(NCAPINTS != 19))
 
 #define cpu_has(c, bit)							\
diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index a5ea841cc6d2..8a2eafa86739 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -84,6 +84,5 @@
 #define DISABLED_MASK16	(DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP)
 #define DISABLED_MASK17	0
 #define DISABLED_MASK18	0
-#define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)
 
 #endif /* _ASM_X86_DISABLED_FEATURES_H */
diff --git a/arch/x86/include/asm/required-features.h b/arch/x86/include/asm/required-features.h
index 6847d85400a8..cb98b66d3e81 100644
--- a/arch/x86/include/asm/required-features.h
+++ b/arch/x86/include/asm/required-features.h
@@ -1,7 +1,7 @@
 #ifndef _ASM_X86_REQUIRED_FEATURES_H
 #define _ASM_X86_REQUIRED_FEATURES_H
 
-/* Define minimum CPUID feature set for kernel These bits are checked
+/* Define minimum CPUID feature set for kernel. These bits are checked
    really early to actually display a visible error message before the
    kernel dies.  Make sure to assign features to the proper mask!
 
@@ -101,6 +101,5 @@
 #define REQUIRED_MASK16	0
 #define REQUIRED_MASK17	0
 #define REQUIRED_MASK18	0
-#define REQUIRED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)
 
 #endif /* _ASM_X86_REQUIRED_FEATURES_H */
-- 
2.17.0

Re: [PATCH] x86/cpufeature: drop *_MASK_CEHCK

[Borislav Petkov]

On Tue, Aug 27, 2019 at 03:05:50PM +0800, Cao jin wrote:
> They are wrappers of BUILD_BUG_ON_ZERO(NCAPINTS != n), which is already
> present in corresponding *_MASK_BIT_SET. And fill the missing period in
> head comments by the way.
> 
> Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
> ---
>  arch/x86/include/asm/cpufeature.h        | 2 --
>  arch/x86/include/asm/disabled-features.h | 1 -
>  arch/x86/include/asm/required-features.h | 3 +--
>  3 files changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> index 58acda503817..232ffb88039c 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -81,7 +81,6 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
>  	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 16, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 17, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 18, feature_bit) ||	\
> -	   REQUIRED_MASK_CHECK					  ||	\
>  	   BUILD_BUG_ON_ZERO(NCAPINTS != 19))
>  
>  #define DISABLED_MASK_BIT_SET(feature_bit)				\
> @@ -104,7 +103,6 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 16, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 17, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 18, feature_bit) ||	\
> -	   DISABLED_MASK_CHECK					  ||	\
>  	   BUILD_BUG_ON_ZERO(NCAPINTS != 19))
>  
>  #define cpu_has(c, bit)							\

If you do a little bit of git archeology:

$ git annotate arch/x86/include/asm/cpufeature.h

after a while, you'll see that this was added in:

1e61f78baf89 ("x86/cpufeature: Make sure DISABLED/REQUIRED macros are updated")

and then you could Cc Dave and ask what he was thinking then?

Leaving in the rest for reference.

> diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
> index a5ea841cc6d2..8a2eafa86739 100644
> --- a/arch/x86/include/asm/disabled-features.h
> +++ b/arch/x86/include/asm/disabled-features.h
> @@ -84,6 +84,5 @@
>  #define DISABLED_MASK16	(DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP)
>  #define DISABLED_MASK17	0
>  #define DISABLED_MASK18	0
> -#define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)
>  
>  #endif /* _ASM_X86_DISABLED_FEATURES_H */
> diff --git a/arch/x86/include/asm/required-features.h b/arch/x86/include/asm/required-features.h
> index 6847d85400a8..cb98b66d3e81 100644
> --- a/arch/x86/include/asm/required-features.h
> +++ b/arch/x86/include/asm/required-features.h
> @@ -1,7 +1,7 @@
>  #ifndef _ASM_X86_REQUIRED_FEATURES_H
>  #define _ASM_X86_REQUIRED_FEATURES_H
>  
> -/* Define minimum CPUID feature set for kernel These bits are checked
> +/* Define minimum CPUID feature set for kernel. These bits are checked
>     really early to actually display a visible error message before the
>     kernel dies.  Make sure to assign features to the proper mask!
>  
> @@ -101,6 +101,5 @@
>  #define REQUIRED_MASK16	0
>  #define REQUIRED_MASK17	0
>  #define REQUIRED_MASK18	0
> -#define REQUIRED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)
>  
>  #endif /* _ASM_X86_REQUIRED_FEATURES_H */
> -- 
> 2.17.0

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Re: [PATCH] x86/cpufeature: drop *_MASK_CEHCK

[Dave Hansen]

On 8/27/19 12:41 AM, Borislav Petkov wrote:
>>  #define DISABLED_MASK_BIT_SET(feature_bit)				\
>> @@ -104,7 +103,6 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
>>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 16, feature_bit) ||	\
>>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 17, feature_bit) ||	\
>>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 18, feature_bit) ||	\
>> -	   DISABLED_MASK_CHECK					  ||	\
>>  	   BUILD_BUG_ON_ZERO(NCAPINTS != 19))
>>  
>>  #define cpu_has(c, bit)							\
> If you do a little bit of git archeology:
> 
> $ git annotate arch/x86/include/asm/cpufeature.h
> 
> after a while, you'll see that this was added in:
> 
> 1e61f78baf89 ("x86/cpufeature: Make sure DISABLED/REQUIRED macros are updated")
> 
> and then you could Cc Dave and ask what he was thinking then?
> 
> Leaving in the rest for reference.

The point was that there are 5 files in the code that need to be changed
if you change NCAPINTS:

1. arch/x86/include/asm/required-features.h
2. arch/x86/include/asm/disabled-features.h
3. tools/arch/x86/include/asm/disabled-features.h
4. tools/arch/x86/include/asm/required-features.h
5. arch/x86/include/asm/cpufeature.h (2 sites)

Each of those sites has a compile-time check for NCAPINTS.  The problem
is that the *-features.h code doesn't get compiled directly so a
BUILD_BUG_ON() doesn't work by itself.  So, for the sites there, we put
it somewhere that *will* get compiled: the macros that actually check
the bits.

It looks weird, but the end effect is good: If you change NCAPINTS, you
get compile errors in 5 files and have to go edit those 5 files to fix
it.  Your patch makes it easier to introduce errors and miss one of
those sites.

Re: [PATCH] x86/cpufeature: drop *_MASK_CEHCK

[Borislav Petkov]

On Tue, Aug 27, 2019 at 09:33:11AM -0700, Dave Hansen wrote:
> The point was that there are 5 files in the code that need to be changed
> if you change NCAPINTS:
> 
> 1. arch/x86/include/asm/required-features.h
> 2. arch/x86/include/asm/disabled-features.h
> 3. tools/arch/x86/include/asm/disabled-features.h
> 4. tools/arch/x86/include/asm/required-features.h
> 5. arch/x86/include/asm/cpufeature.h (2 sites)
> 
> Each of those sites has a compile-time check for NCAPINTS.  The problem
> is that the *-features.h code doesn't get compiled directly so a
> BUILD_BUG_ON() doesn't work by itself.  So, for the sites there, we put
> it somewhere that *will* get compiled: the macros that actually check
> the bits.
> 
> It looks weird, but the end effect is good: If you change NCAPINTS, you
> get compile errors in 5 files and have to go edit those 5 files to fix
> it.  Your patch makes it easier to introduce errors and miss one of
> those sites.

... and we wouldn't want to debug any strange bugs from missing a case.
So, Cao, I wouldn't mind having the gist of that above somewhere around
there in a comment explicitly.

Thx.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Re: [PATCH] x86/cpufeature: drop *_MASK_CEHCK

[Cao jin]

On 8/28/19 1:20 AM, Borislav Petkov wrote:
> On Tue, Aug 27, 2019 at 09:33:11AM -0700, Dave Hansen wrote:
>> The point was that there are 5 files in the code that need to be changed
>> if you change NCAPINTS:
>>
>> 1. arch/x86/include/asm/required-features.h
>> 2. arch/x86/include/asm/disabled-features.h
>> 3. tools/arch/x86/include/asm/disabled-features.h
>> 4. tools/arch/x86/include/asm/required-features.h
>> 5. arch/x86/include/asm/cpufeature.h (2 sites)
>>
>> Each of those sites has a compile-time check for NCAPINTS.  The problem
>> is that the *-features.h code doesn't get compiled directly so a
>> BUILD_BUG_ON() doesn't work by itself.  So, for the sites there, we put
>> it somewhere that *will* get compiled: the macros that actually check
>> the bits.
>>
>> It looks weird, but the end effect is good: If you change NCAPINTS, you
>> get compile errors in 5 files and have to go edit those 5 files to fix
>> it.  Your patch makes it easier to introduce errors and miss one of
>> those sites.
> 
> ... and we wouldn't want to debug any strange bugs from missing a case.
> So, Cao, I wouldn't mind having the gist of that above somewhere around
> there in a comment explicitly.
> 

A subtle issue hard to detect by eyes.  Sure, on the way.
-- 
Sincerely,
Cao jin