3 files changed, 46 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 7116fda7077f..06600cc9a26c 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 100a9a10076a..f0d0b20fe149 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/intel.c b/arch/x86/kernel/cpu/intel.c
index 34bbb555e269..897d6201ef10 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -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
@@ -214,6 +222,17 @@ 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.
          */