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SubjectRe: Re: [PATCH] x86: set Pentium M as PAE capable
On Mon, Mar 03, 2014 at 09:04:19PM -0800, H. Peter Anvin wrote:
> forcepae is descriptive.

Back to forcepae.

Signed-off-by: Chris Bainbridge <chris.bainbridge@gmail.com>
---
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 580a60c..67755ea 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -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
diff --git a/arch/x86/boot/cpucheck.c b/arch/x86/boot/cpucheck.c
index 100a9a1..f0d0b20 100644
--- a/arch/x86/boot/cpucheck.c
+++ b/arch/x86/boot/cpucheck.c
@@ -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)
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index c67ffa6..7ec4119 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -218,7 +218,7 @@ static void amd_k7_smp_check(struct cpuinfo_x86 *c)
*/
WARN_ONCE(1, "WARNING: This combination of AMD"
" processors is not suitable for SMP.\n");
- add_taint(TAINT_UNSAFE_SMP, LOCKDEP_NOW_UNRELIABLE);
+ add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_NOW_UNRELIABLE);
}

static void init_amd_k7(struct cpuinfo_x86 *c)
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index ea56e7c..053cb59 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -195,6 +195,14 @@ 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)
{
unsigned long lo, hi;
@@ -225,6 +233,17 @@ static void intel_workarounds(struct cpuinfo_x86 *c)
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.
*/
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 196d1ea..08fb024 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -458,7 +458,7 @@ extern enum system_states {

#define TAINT_PROPRIETARY_MODULE 0
#define TAINT_FORCED_MODULE 1
-#define TAINT_UNSAFE_SMP 2
+#define TAINT_CPU_OUT_OF_SPEC 2
#define TAINT_FORCED_RMMOD 3
#define TAINT_MACHINE_CHECK 4
#define TAINT_BAD_PAGE 5
diff --git a/kernel/module.c b/kernel/module.c
index b99e801..8dc7f5e 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1015,7 +1015,7 @@ static size_t module_flags_taint(struct module *mod, char *buf)
buf[l++] = 'C';
/*
* TAINT_FORCED_RMMOD: could be added.
- * TAINT_UNSAFE_SMP, TAINT_MACHINE_CHECK, TAINT_BAD_PAGE don't
+ * TAINT_CPU_OUT_OF_SPEC, TAINT_MACHINE_CHECK, TAINT_BAD_PAGE don't
* apply to modules.
*/
return l;
diff --git a/kernel/panic.c b/kernel/panic.c
index 3eb0ffb..cca8a91 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -199,7 +199,7 @@ struct tnt {
static const struct tnt tnts[] = {
{ TAINT_PROPRIETARY_MODULE, 'P', 'G' },
{ TAINT_FORCED_MODULE, 'F', ' ' },
- { TAINT_UNSAFE_SMP, 'S', ' ' },
+ { TAINT_CPU_OUT_OF_SPEC, 'S', ' ' },
{ TAINT_FORCED_RMMOD, 'R', ' ' },
{ TAINT_MACHINE_CHECK, 'M', ' ' },
{ TAINT_BAD_PAGE, 'B', ' ' },

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