Prior to 0c2a3913d6f5, clearcpuid= could be specified several times on
the command line to clear several bits. The old multiple option is a
little anachronistic so change clearcpuid to accept a comma-separated
list of numbers. Up to about eight bits can be cleared.
Fixes: 0c2a3913d6f5 ("x86/fpu: Parse clearcpuid= as early XSAVE argument")
Signed-off-by: John Haxby <john.haxby@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
.../admin-guide/kernel-parameters.txt | 24 ++++++++++---------
arch/x86/kernel/fpu/init.c | 18 ++++++++------
2 files changed, 24 insertions(+), 18 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f2a93c8679e8..f380781be9e0 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -577,18 +577,20 @@
loops can be debugged more effectively on production
systems.
- clearcpuid=BITNUM [X86]
- Disable CPUID feature X for the kernel. See
+ clearcpuid=BITNUM[,BITNUM,...] [X86]
+ Disable CPUID features for the kernel. See
arch/x86/include/asm/cpufeatures.h for the valid bit
- numbers. Note the Linux specific bits are not necessarily
- stable over kernel options, but the vendor specific
- ones should be.
- Also note that user programs calling CPUID directly
- or using the feature without checking anything
- will still see it. This just prevents it from
- being used by the kernel or shown in /proc/cpuinfo.
- Also note the kernel might malfunction if you disable
- some critical bits.
+ numbers. Up to about eight bits can be cleared. Note the
+ Linux specific bits are not necessarily stable over
+ kernel options, but the vendor specific ones should be.
+ Also note that user programs calling CPUID directly or
+ using the feature without checking anything will still
+ see it. This just prevents it from being used by the
+ kernel or shown in /proc/cpuinfo. Also note the kernel
+ might malfunction if you disable some critical bits.
+ Consider using a virtual machine emulating an older CPU
+ type for clearing many bits or for making the cleared
+ bits visible to user programs.
cma=nn[MG]@[start[MG][-end[MG]]]
[ARM,X86,KNL]
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 6ce7e0a23268..8d826505c22e 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -243,8 +243,6 @@ static void __init fpu__init_system_ctx_switch(void)
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"))
@@ -268,11 +266,17 @@ static void __init fpu__init_parse_early_param(void)
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);
+ sizeof(arg))) {
+ /* cpuid bit numbers are mostly three digits */
+ enum { nints = sizeof(arg)/(3+1) + 1 };
+ int i, bits[nints];
+
+ get_options(arg, nints, bits);
+ for (i = 1; i <= bits[0]; i++) {
+ if (bits[i] >= 0 && bits[i] < NCAPINTS * 32)
+ setup_clear_cpu_cap(bits[i]);
+ }
+ }
}
/*
--
2.25.3
