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Date: Mon, 17 Jun 2024 12:34:09 -0400
From: Brian Gerst <brgerst@...il.com>
To: "Xin Li (Intel)" <xin@...or.com>
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, will@...nel.org,
peterz@...radead.org, akpm@...ux-foundation.org, acme@...nel.org,
namhyung@...nel.org
Subject: Re: [PATCH v2 2/3] x86/cpufeatures: Generate a feature mask header
based on build config
On Sun, Jun 16, 2024 at 4:58 AM Xin Li (Intel) <xin@...or.com> wrote:
>
> From: "H. Peter Anvin (Intel)" <hpa@...or.com>
>
> Introduce an AWK script to auto-generate a header with required and
> disabled feature masks based on <asm/cpufeatures.h> and current build
> config. Thus for any CPU feature with a build config, e.g., X86_FRED,
> simply add
>
> config X86_DISABLED_FEATURE_FRED
> def_bool y
> depends on !X86_FRED
>
> to arch/x86/Kconfig.cpufeatures, instead of adding a conditional CPU
> feature disable flag, e.g., DISABLE_FRED.
>
> Lastly the generated required and disabled feature masks will be added
> to their corresponding feature masks for this particular compile-time
> configuration.
>
> [ Xin: build integration improvements ]
>
> Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
> Signed-off-by: Xin Li (Intel) <xin@...or.com>
> ---
>
> Change since v1:
> * Remove code generating unused macros {REQUIRED,DISABLED}_FEATURE(x)
> to tell if a CPU feature, e.g., X86_FEATURE_FRED, is a required or
> disabled feature for this particular compile-time configuration.
> ---
> arch/x86/Makefile | 17 +++++-
> arch/x86/boot/cpucheck.c | 3 +-
> arch/x86/boot/cpuflags.c | 1 -
> arch/x86/boot/mkcpustr.c | 3 +-
> arch/x86/include/asm/Kbuild | 1 +
> arch/x86/include/asm/cpufeature.h | 1 +
> arch/x86/include/asm/cpufeatures.h | 8 ---
> arch/x86/kernel/verify_cpu.S | 1 +
> arch/x86/tools/featuremasks.awk | 90 ++++++++++++++++++++++++++++++
> 9 files changed, 111 insertions(+), 14 deletions(-)
> create mode 100755 arch/x86/tools/featuremasks.awk
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 801fd85c3ef6..211c0820b150 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -261,9 +261,22 @@ archscripts: scripts_basic
> $(Q)$(MAKE) $(build)=arch/x86/tools relocs
>
> ###
> -# Syscall table generation
> +# Feature masks header and syscall table generation
>
> -archheaders:
> +out := arch/x86/include/generated/asm
> +featuremasks_hdr := featuremasks.h
> +featuremasks_awk := $(srctree)/arch/x86/tools/featuremasks.awk
> +cpufeatures_hdr := $(srctree)/arch/x86/include/asm/cpufeatures.h
> +quiet_cmd_gen_featuremasks = GEN $@
> + cmd_gen_featuremasks = $(AWK) -f $(featuremasks_awk) $(cpufeatures_hdr) $(KCONFIG_CONFIG) > $@
> +
> +$(out)/$(featuremasks_hdr): $(featuremasks_awk) $(cpufeatures_hdr) $(KCONFIG_CONFIG) FORCE
> + $(shell mkdir -p $(out))
> + $(call if_changed,gen_featuremasks)
> +
> +targets += $(out)/$(featuremasks_hdr)
> +
> +archheaders: $(out)/$(featuremasks_hdr)
> $(Q)$(MAKE) $(build)=arch/x86/entry/syscalls all
>
> ###
> diff --git a/arch/x86/boot/cpucheck.c b/arch/x86/boot/cpucheck.c
> index 0aae4d4ed615..8d03a741d1b2 100644
> --- a/arch/x86/boot/cpucheck.c
> +++ b/arch/x86/boot/cpucheck.c
> @@ -22,10 +22,11 @@
> # include "boot.h"
> #endif
> #include <linux/types.h>
> +#include <asm/featuremasks.h>
> #include <asm/intel-family.h>
> #include <asm/processor-flags.h>
> -#include <asm/required-features.h>
> #include <asm/msr-index.h>
> +
> #include "string.h"
> #include "msr.h"
>
> diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
> index d75237ba7ce9..0cabdacb2a2f 100644
> --- a/arch/x86/boot/cpuflags.c
> +++ b/arch/x86/boot/cpuflags.c
> @@ -3,7 +3,6 @@
> #include "bitops.h"
>
> #include <asm/processor-flags.h>
> -#include <asm/required-features.h>
> #include <asm/msr-index.h>
> #include "cpuflags.h"
>
> diff --git a/arch/x86/boot/mkcpustr.c b/arch/x86/boot/mkcpustr.c
> index da0ccc5de538..b90110109675 100644
> --- a/arch/x86/boot/mkcpustr.c
> +++ b/arch/x86/boot/mkcpustr.c
> @@ -12,8 +12,6 @@
>
> #include <stdio.h>
>
> -#include "../include/asm/required-features.h"
> -#include "../include/asm/disabled-features.h"
> #include "../include/asm/cpufeatures.h"
> #include "../include/asm/vmxfeatures.h"
> #include "../kernel/cpu/capflags.c"
> @@ -23,6 +21,7 @@ int main(void)
> int i, j;
> const char *str;
>
> + printf("#include <asm/featuremasks.h>\n\n");
> printf("static const char x86_cap_strs[] =\n");
>
> for (i = 0; i < NCAPINTS; i++) {
> diff --git a/arch/x86/include/asm/Kbuild b/arch/x86/include/asm/Kbuild
> index a192bdea69e2..29c3481f40fc 100644
> --- a/arch/x86/include/asm/Kbuild
> +++ b/arch/x86/include/asm/Kbuild
> @@ -8,6 +8,7 @@ generated-y += syscalls_x32.h
> generated-y += unistd_32_ia32.h
> generated-y += unistd_64_x32.h
> generated-y += xen-hypercalls.h
> +generated-y += featuremasks.h
>
> generic-y += early_ioremap.h
> generic-y += mcs_spinlock.h
> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> index 0b9611da6c53..8332f596ba3c 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -9,6 +9,7 @@
> #include <asm/asm.h>
> #include <linux/bitops.h>
> #include <asm/alternative.h>
> +#include <asm/featuremasks.h>
>
> enum cpuid_leafs
> {
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 3c7434329661..05503448b94d 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -2,14 +2,6 @@
> #ifndef _ASM_X86_CPUFEATURES_H
> #define _ASM_X86_CPUFEATURES_H
>
> -#ifndef _ASM_X86_REQUIRED_FEATURES_H
> -#include <asm/required-features.h>
> -#endif
> -
> -#ifndef _ASM_X86_DISABLED_FEATURES_H
> -#include <asm/disabled-features.h>
> -#endif
> -
> /*
> * Defines x86 CPU feature bits
> */
> diff --git a/arch/x86/kernel/verify_cpu.S b/arch/x86/kernel/verify_cpu.S
> index 1258a5872d12..3205cbb47b9c 100644
> --- a/arch/x86/kernel/verify_cpu.S
> +++ b/arch/x86/kernel/verify_cpu.S
> @@ -29,6 +29,7 @@
> */
>
> #include <asm/cpufeatures.h>
> +#include <asm/featuremasks.h>
> #include <asm/msr-index.h>
>
> SYM_FUNC_START_LOCAL(verify_cpu)
> diff --git a/arch/x86/tools/featuremasks.awk b/arch/x86/tools/featuremasks.awk
> new file mode 100755
> index 000000000000..c96e6cf43161
> --- /dev/null
> +++ b/arch/x86/tools/featuremasks.awk
> @@ -0,0 +1,90 @@
> +#!/usr/bin/awk
> +#
> +# Convert cpufeatures.h to a list of compile-time masks
> +# Note: this blithly assumes that each word has at least one
> +# feature defined in it; if not, something else is wrong!
> +#
> +
> +BEGIN {
> + printf "#ifndef _ASM_X86_FEATUREMASKS_H\n";
> + printf "#define _ASM_X86_FEATUREMASKS_H\n\n";
> +
> + file = 0
> +}
> +
> +BEGINFILE {
> + switch (++file) {
> + case 1: # cpufeatures.h
> + FPAT = "#[ \t]*[a-z]+|[A-Za-z0-9_]+|[^ \t]";
> + break;
> + case 2: # .config
> + FPAT = "CONFIG_[A-Z0-9_]+|is not set|[yn]";
> + break;
> + }
> +}
> +
> +file == 1 && $1 ~ /^#[ \t]*define$/ && $2 ~ /^X86_FEATURE_/ &&
> +$3 == "(" && $5 == "*" && $7 == "+" && $9 == ")" {
> + nfeat = $4 * $6 + $8;
> + feat = $2;
> + sub(/^X86_FEATURE_/, "", feat);
> + feats[nfeat] = feat;
> +}
> +file == 1 && $1 ~ /^#[ \t]*define$/ && $2 == "NCAPINTS" {
> + ncapints = strtonum($3);
> +}
> +
> +file == 2 && $1 ~ /^CONFIG_X86_[A-Z]*_FEATURE_/ {
> + on = ($2 == "y");
> + printf "/* %s = %s (%d) */\n", $1, $2, on;
This looks like extra debugging output that doesn't need to be in the
final release.
> + if (split($1, fs, "CONFIG_X86_|_FEATURE_") == 3) {
> + printf "/* %s %s = %d */\n", fs[2], fs[3], on;
Same.
> + featstat[fs[2], fs[3]] = on;
> + }
> +}
> +
> +END {
> + sets[1] = "REQUIRED";
> + sets[2] = "DISABLED";
> +
> + for (ns in sets) {
> + s = sets[ns];
> +
> + printf "/*\n";
> + printf " * %s features:\n", s;
> + printf " *\n";
> + fstr = "";
> + for (i = 0; i < ncapints; i++) {
> + mask = 0;
> + for (j = 0; j < 32; j++) {
> + nfeat = i*32 + j;
> + feat = feats[nfeat];
> + if (feat) {
> + st = !!featstat[s, feat];
> + if (st) {
> + nfstr = fstr " " feat;
> + if (length(nfstr) > 72) {
> + printf " * %s\n", fstr;
> + nfstr = " " feat;
> + }
> + fstr = nfstr;
> + }
> + mask += st * (2 ^ j);
> + }
> + }
> + masks[i] = mask;
> + }
> + printf " * %s\n */\n\n", fstr;
> +
> + for (i = 0; i < ncapints; i++) {
> + printf "#define %s_MASK%-3d 0x%08x\n", s, i, masks[i];
> + }
> +
> + printf "#define %s_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != %d)\n\n", s, ncapints;
> + }
> +
> + printf "#define SSE_MASK\t\\\n";
> + printf "\t(REQUIRED_MASK0 & ((1<<(X86_FEATURE_XMM & 31)) | (1<<(X86_FEATURE_XMM2 & 31))))\n\n";
This could be moved to verify_cpu.S, since that is the only place it is used.
> + printf "#endif /* _ASM_X86_FEATUREMASKS_H */\n";
> +}
> --
> 2.45.1
>
>
You could also generate {REQUIRED|DISABLED}_MASK_BIT_SET() in this
script, so that they are always in sync with NCAPINTS.
Brian Gerst
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