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* Allow clearcpuid= to accept multiple bits, by Arvind Sankar.

Browse Source 
* Move clearcpuid= parameter handling earlier in the boot, away from the
 FPU init code and to a generic location, by Mike Hommey.
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Merge tag 'x86_fpu_for_v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fpu updates from Borislav Petkov:

 - Allow clearcpuid= to accept multiple bits (Arvind Sankar)

 - Move clearcpuid= parameter handling earlier in the boot, away from
   the FPU init code and to a generic location (Mike Hommey)

* tag 'x86_fpu_for_v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/fpu: Handle FPU-related and clearcpuid command line arguments earlier
  x86/fpu: Allow multiple bits in clearcpuid= parameter
This commit is contained in:
Linus Torvalds 2020-10-12 10:49:46 -07:00
commit a0d445f70c
3 changed files with 56 additions and 42 deletions
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2
Documentation/admin-guide/kernel-parameters.txt
View File

@ -577,7 +577,7 @@
loops can be debugged more effectively on production
systems.
clearcpuid=BITNUM [X86]
clearcpuid=BITNUM[,BITNUM...] [X86]
Disable CPUID feature X for the kernel. See
arch/x86/include/asm/cpufeatures.h for the valid bit
numbers. Note the Linux specific bits are not necessarily

55
arch/x86/kernel/cpu/common.c
View File

@ -23,6 +23,7 @@
#include <linux/syscore_ops.h>
#include <linux/pgtable.h>
#include <asm/cmdline.h>
#include <asm/stackprotector.h>
#include <asm/perf_event.h>
#include <asm/mmu_context.h>
@ -1220,6 +1221,59 @@ static void detect_nopl(void)
#endif
}
/*
* We parse cpu parameters early because fpu__init_system() is executed
* before parse_early_param().
*/
static void __init cpu_parse_early_param(void)
{
char arg[128];
char *argptr = arg;
int arglen, res, bit;
#ifdef CONFIG_X86_32
if (cmdline_find_option_bool(boot_command_line, "no387"))
#ifdef CONFIG_MATH_EMULATION
setup_clear_cpu_cap(X86_FEATURE_FPU);
#else
pr_err("Option 'no387' required CONFIG_MATH_EMULATION enabled.\n");
#endif
if (cmdline_find_option_bool(boot_command_line, "nofxsr"))
setup_clear_cpu_cap(X86_FEATURE_FXSR);
#endif
if (cmdline_find_option_bool(boot_command_line, "noxsave"))
setup_clear_cpu_cap(X86_FEATURE_XSAVE);
if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
setup_clear_cpu_cap(X86_FEATURE_XSAVES);
arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
if (arglen <= 0)
return;
pr_info("Clearing CPUID bits:");
do {
res = get_option(&argptr, &bit);
if (res == 0 || res == 3)
break;
/* If the argument was too long, the last bit may be cut off */
if (res == 1 && arglen >= sizeof(arg))
break;
if (bit >= 0 && bit < NCAPINTS * 32) {
pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit));
setup_clear_cpu_cap(bit);
}
} while (res == 2);
pr_cont("\n");
}
/*
* Do minimum CPU detection early.
* Fields really needed: vendor, cpuid_level, family, model, mask,
@ -1255,6 +1309,7 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
get_cpu_cap(c);
get_cpu_address_sizes(c);
setup_force_cpu_cap(X86_FEATURE_CPUID);
cpu_parse_early_param();
if (this_cpu->c_early_init)
this_cpu->c_early_init(c);

41
arch/x86/kernel/fpu/init.c
View File

@ -5,7 +5,6 @@
#include <asm/fpu/internal.h>
#include <asm/tlbflush.h>
#include <asm/setup.h>
#include <asm/cmdline.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
@ -237,52 +236,12 @@ static void __init fpu__init_system_ctx_switch(void)
on_boot_cpu = 0;
}
/*
* We parse fpu parameters early because fpu__init_system() is executed
* before parse_early_param().
*/
static void __init fpu__init_parse_early_param(void)
{
char arg[32];
char *argptr = arg;
int bit;
#ifdef CONFIG_X86_32
if (cmdline_find_option_bool(boot_command_line, "no387"))
#ifdef CONFIG_MATH_EMULATION
setup_clear_cpu_cap(X86_FEATURE_FPU);
#else
pr_err("Option 'no387' required CONFIG_MATH_EMULATION enabled.\n");
#endif
if (cmdline_find_option_bool(boot_command_line, "nofxsr"))
setup_clear_cpu_cap(X86_FEATURE_FXSR);
#endif
if (cmdline_find_option_bool(boot_command_line, "noxsave"))
setup_clear_cpu_cap(X86_FEATURE_XSAVE);
if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
setup_clear_cpu_cap(X86_FEATURE_XSAVES);
if (cmdline_find_option(boot_command_line, "clearcpuid", arg,
sizeof(arg)) &&
get_option(&argptr, &bit) &&
bit >= 0 &&
bit < NCAPINTS * 32)
setup_clear_cpu_cap(bit);
}
/*
* Called on the boot CPU once per system bootup, to set up the initial
* FPU state that is later cloned into all processes:
*/
void __init fpu__init_system(struct cpuinfo_x86 *c)
{
fpu__init_parse_early_param();
fpu__init_system_early_generic(c);
/*