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linux-next/arch/x86/include/asm/cpufeature.h
Cao Jin cbb1133b56 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@alien8.de>
Signed-off-by: Cao Jin <caoj.fnst@cn.fujitsu.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nadav Amit <namit@vmware.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190828061100.27032-1-caoj.fnst@cn.fujitsu.com
2019-08-28 08:38:39 +02:00

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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_X86_CPUFEATURE_H
#define _ASM_X86_CPUFEATURE_H
#include <asm/processor.h>
#if defined(__KERNEL__) && !defined(__ASSEMBLY__)
#include <asm/asm.h>
#include <linux/bitops.h>
enum cpuid_leafs
{
CPUID_1_EDX = 0,
CPUID_8000_0001_EDX,
CPUID_8086_0001_EDX,
CPUID_LNX_1,
CPUID_1_ECX,
CPUID_C000_0001_EDX,
CPUID_8000_0001_ECX,
CPUID_LNX_2,
CPUID_LNX_3,
CPUID_7_0_EBX,
CPUID_D_1_EAX,
CPUID_LNX_4,
CPUID_7_1_EAX,
CPUID_8000_0008_EBX,
CPUID_6_EAX,
CPUID_8000_000A_EDX,
CPUID_7_ECX,
CPUID_8000_0007_EBX,
CPUID_7_EDX,
};
#ifdef CONFIG_X86_FEATURE_NAMES
extern const char * const x86_cap_flags[NCAPINTS*32];
extern const char * const x86_power_flags[32];
#define X86_CAP_FMT "%s"
#define x86_cap_flag(flag) x86_cap_flags[flag]
#else
#define X86_CAP_FMT "%d:%d"
#define x86_cap_flag(flag) ((flag) >> 5), ((flag) & 31)
#endif
/*
* In order to save room, we index into this array by doing
* X86_BUG_<name> - NCAPINTS*32.
*/
extern const char * const x86_bug_flags[NBUGINTS*32];
#define test_cpu_cap(c, bit) \
test_bit(bit, (unsigned long *)((c)->x86_capability))
/*
* There are 32 bits/features in each mask word. The high bits
* (selected with (bit>>5) give us the word number and the low 5
* bits give us the bit/feature number inside the word.
* (1UL<<((bit)&31) gives us a mask for the feature_bit so we can
* see if it is set in the mask word.
*/
#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) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 2, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 3, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 4, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 5, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 6, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 7, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 8, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 9, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 10, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 11, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 12, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 13, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 14, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 15, feature_bit) || \
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) \
( CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 0, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 1, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 2, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 3, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 4, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 5, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 6, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 7, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 8, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 9, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 10, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 11, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 12, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 13, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 14, feature_bit) || \
CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 15, feature_bit) || \
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) \
(__builtin_constant_p(bit) && REQUIRED_MASK_BIT_SET(bit) ? 1 : \
test_cpu_cap(c, bit))
#define this_cpu_has(bit) \
(__builtin_constant_p(bit) && REQUIRED_MASK_BIT_SET(bit) ? 1 : \
x86_this_cpu_test_bit(bit, \
(unsigned long __percpu *)&cpu_info.x86_capability))
/*
* This macro is for detection of features which need kernel
* infrastructure to be used. It may *not* directly test the CPU
* itself. Use the cpu_has() family if you want true runtime
* testing of CPU features, like in hypervisor code where you are
* supporting a possible guest feature where host support for it
* is not relevant.
*/
#define cpu_feature_enabled(bit) \
(__builtin_constant_p(bit) && DISABLED_MASK_BIT_SET(bit) ? 0 : static_cpu_has(bit))
#define boot_cpu_has(bit) cpu_has(&boot_cpu_data, bit)
#define set_cpu_cap(c, bit) set_bit(bit, (unsigned long *)((c)->x86_capability))
extern void setup_clear_cpu_cap(unsigned int bit);
extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
#define setup_force_cpu_cap(bit) do { \
set_cpu_cap(&boot_cpu_data, bit); \
set_bit(bit, (unsigned long *)cpu_caps_set); \
} while (0)
#define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
#if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
/*
* Workaround for the sake of BPF compilation which utilizes kernel
* headers, but clang does not support ASM GOTO and fails the build.
*/
#ifndef __BPF_TRACING__
#warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
#endif
#define static_cpu_has(bit) boot_cpu_has(bit)
#else
/*
* Static testing of CPU features. Used the same as boot_cpu_has(). It
* statically patches the target code for additional performance. Use
* static_cpu_has() only in fast paths, where every cycle counts. Which
* means that the boot_cpu_has() variant is already fast enough for the
* majority of cases and you should stick to using it as it is generally
* only two instructions: a RIP-relative MOV and a TEST.
*/
static __always_inline bool _static_cpu_has(u16 bit)
{
asm_volatile_goto("1: jmp 6f\n"
"2:\n"
".skip -(((5f-4f) - (2b-1b)) > 0) * "
"((5f-4f) - (2b-1b)),0x90\n"
"3:\n"
".section .altinstructions,\"a\"\n"
" .long 1b - .\n" /* src offset */
" .long 4f - .\n" /* repl offset */
" .word %P[always]\n" /* always replace */
" .byte 3b - 1b\n" /* src len */
" .byte 5f - 4f\n" /* repl len */
" .byte 3b - 2b\n" /* pad len */
".previous\n"
".section .altinstr_replacement,\"ax\"\n"
"4: jmp %l[t_no]\n"
"5:\n"
".previous\n"
".section .altinstructions,\"a\"\n"
" .long 1b - .\n" /* src offset */
" .long 0\n" /* no replacement */
" .word %P[feature]\n" /* feature bit */
" .byte 3b - 1b\n" /* src len */
" .byte 0\n" /* repl len */
" .byte 0\n" /* pad len */
".previous\n"
".section .altinstr_aux,\"ax\"\n"
"6:\n"
" testb %[bitnum],%[cap_byte]\n"
" jnz %l[t_yes]\n"
" jmp %l[t_no]\n"
".previous\n"
: : [feature] "i" (bit),
[always] "i" (X86_FEATURE_ALWAYS),
[bitnum] "i" (1 << (bit & 7)),
[cap_byte] "m" (((const char *)boot_cpu_data.x86_capability)[bit >> 3])
: : t_yes, t_no);
t_yes:
return true;
t_no:
return false;
}
#define static_cpu_has(bit) \
( \
__builtin_constant_p(boot_cpu_has(bit)) ? \
boot_cpu_has(bit) : \
_static_cpu_has(bit) \
)
#endif
#define cpu_has_bug(c, bit) cpu_has(c, (bit))
#define set_cpu_bug(c, bit) set_cpu_cap(c, (bit))
#define clear_cpu_bug(c, bit) clear_cpu_cap(c, (bit))
#define static_cpu_has_bug(bit) static_cpu_has((bit))
#define boot_cpu_has_bug(bit) cpu_has_bug(&boot_cpu_data, (bit))
#define boot_cpu_set_bug(bit) set_cpu_cap(&boot_cpu_data, (bit))
#define MAX_CPU_FEATURES (NCAPINTS * 32)
#define cpu_have_feature boot_cpu_has
#define CPU_FEATURE_TYPEFMT "x86,ven%04Xfam%04Xmod%04X"
#define CPU_FEATURE_TYPEVAL boot_cpu_data.x86_vendor, boot_cpu_data.x86, \
boot_cpu_data.x86_model
#endif /* defined(__KERNEL__) && !defined(__ASSEMBLY__) */
#endif /* _ASM_X86_CPUFEATURE_H */
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