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x86, cpu: Add forcepae parameter for booting PAE kernels on PAE-disabled Pentium M

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Many Pentium M systems disable PAE but may have a functionally usable PAE
implementation. This adds the "forcepae" parameter which bypasses the boot
check for PAE, and sets the CPU as being PAE capable. Using this parameter
will taint the kernel with TAINT_CPU_OUT_OF_SPEC.

Signed-off-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Link: http://lkml.kernel.org/r/20140307114040.GA4997@localhost
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Chris Bainbridge 2014-03-07 18:40:42 +07:00 committed by H. Peter Anvin
parent 8c90487cdc
commit 69f2366c94
3 changed files with 46 additions and 0 deletions
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7
Documentation/kernel-parameters.txt
View file

@ -1011,6 +1011,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
parameter will force ia64_sal_cache_flush to call
ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
forcepae [X86-32]
Forcefully enable Physical Address Extension (PAE).
Many Pentium M systems disable PAE but may have a
functionally usable PAE implementation.
Warning: use of this parameter will taint the kernel
and may cause unknown problems.
ftrace=[tracer]
[FTRACE] will set and start the specified tracer
as early as possible in order to facilitate early

20
arch/x86/boot/cpucheck.c
View file

@ -67,6 +67,13 @@ static int is_transmeta(void)
cpu_vendor[2] == A32('M', 'x', '8', '6');
}
static int is_intel(void)
{
return cpu_vendor[0] == A32('G', 'e', 'n', 'u') &&
cpu_vendor[1] == A32('i', 'n', 'e', 'I') &&
cpu_vendor[2] == A32('n', 't', 'e', 'l');
}
/* Returns a bitmask of which words we have error bits in */
static int check_cpuflags(void)
{
@ -153,6 +160,19 @@ int check_cpu(int *cpu_level_ptr, int *req_level_ptr, u32 **err_flags_ptr)
asm("wrmsr" : : "a" (eax), "d" (edx), "c" (ecx));
err = check_cpuflags();
} else if (err == 0x01 &&
!(err_flags[0] & ~(1 << X86_FEATURE_PAE)) &&
is_intel() && cpu.level == 6 &&
(cpu.model == 9 || cpu.model == 13)) {
/* PAE is disabled on this Pentium M but can be forced */
if (cmdline_find_option_bool("forcepae")) {
puts("WARNING: Forcing PAE in CPU flags\n");
set_bit(X86_FEATURE_PAE, cpu.flags);
err = check_cpuflags();
}
else {
puts("WARNING: PAE disabled. Use parameter 'forcepae' to enable at your own risk!\n");
}
}
if (err_flags_ptr)

19
arch/x86/kernel/cpu/intel.c
View file

@ -186,6 +186,14 @@ static void intel_smp_check(struct cpuinfo_x86 *c)
}
}
static int forcepae;
static int __init forcepae_setup(char *__unused)
{
forcepae = 1;
return 1;
}
__setup("forcepae", forcepae_setup);
static void intel_workarounds(struct cpuinfo_x86 *c)
{
#ifdef CONFIG_X86_F00F_BUG
@ -213,6 +221,17 @@ static void intel_workarounds(struct cpuinfo_x86 *c)
if ((c->x86<<8 | c->x86_model<<4 | c->x86_mask) < 0x633)
clear_cpu_cap(c, X86_FEATURE_SEP);
/*
* PAE CPUID issue: many Pentium M report no PAE but may have a
* functionally usable PAE implementation.
* Forcefully enable PAE if kernel parameter "forcepae" is present.
*/
if (forcepae) {
printk(KERN_WARNING "PAE forced!\n");
set_cpu_cap(c, X86_FEATURE_PAE);
add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_NOW_UNRELIABLE);
}
/*
* P4 Xeon errata 037 workaround.
* Hardware prefetcher may cause stale data to be loaded into the cache.