linux-kernel - [tip: x86/cleanups] x86/cpufeature: Explain the macro duplication

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Message-ID: <156697495154.15133.9156303181767258276.tip-bot2@tip-bot2>
Date:   Wed, 28 Aug 2019 06:49:11 -0000
From:   "tip-bot2 for Cao Jin" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Borislav Petkov <bp@...en8.de>, Cao Jin <caoj.fnst@...fujitsu.com>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jann Horn <jannh@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nadav Amit <namit@...are.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "x86-ml" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/cleanups] x86/cpufeature: Explain the macro duplication

The following commit has been merged into the x86/cleanups branch of tip:

Commit-ID:     cbb1133b563a63901cf778220eb17e3ff1425aed
Gitweb:        https://git.kernel.org/tip/cbb1133b563a63901cf778220eb17e3ff1425aed
Author:        Cao Jin <caoj.fnst@...fujitsu.com>
AuthorDate:    Wed, 28 Aug 2019 14:11:00 +08:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Wed, 28 Aug 2019 08:38:39 +02:00

x86/cpufeature: Explain the macro duplication

Explain the intent behind the duplication of the

  BUILD_BUG_ON_ZERO(NCAPINTS != n)

check in *_MASK_CHECK and its immediate use in the *MASK_BIT_SET macros
too.

 [ bp: Massage. ]

Suggested-by: Borislav Petkov <bp@...en8.de>
Signed-off-by: Cao Jin <caoj.fnst@...fujitsu.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Jann Horn <jannh@...gle.com>
Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Nadav Amit <namit@...are.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: x86-ml <x86@...nel.org>
Link: https://lkml.kernel.org/r/20190828061100.27032-1-caoj.fnst@cn.fujitsu.com
---
 arch/x86/include/asm/cpufeature.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 58acda5..59bf91c 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -61,6 +61,13 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
 #define CHECK_BIT_IN_MASK_WORD(maskname, word, bit)	\
 	(((bit)>>5)==(word) && (1UL<<((bit)&31) & maskname##word ))
 
+/*
+ * {REQUIRED,DISABLED}_MASK_CHECK below may seem duplicated with the
+ * following BUILD_BUG_ON_ZERO() check but when NCAPINTS gets changed, all
+ * header macros which use NCAPINTS need to be changed. The duplicated macro
+ * use causes the compiler to issue errors for all headers so that all usage
+ * sites can be corrected.
+ */
 #define REQUIRED_MASK_BIT_SET(feature_bit)		\
 	 ( CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK,  0, feature_bit) ||	\
 	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK,  1, feature_bit) ||	\