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SubjectRe: [PATCH] x86: set Pentium M as PAE capable
On Fri, Feb 28, 2014 at 03:27:50PM +0300, Dennis Mungai wrote:
> Hello people,
>
> Note that revisions of the Dothan core were released in the first quarter
> of 2005 with the *Sonoma* chipsets and supported a 533 MT/s FSB and NX-bit
> (and PAE support required for it was enabled, unlike earlier Pentium Ms
> that had it disabled). These processors include the 730M (1.6 GHz), 740M
> (1.73 GHz), 750M (1.86 GHz), 760M (2.0 GHz) and 770M (2.13 GHz). These
> models all have a TDP of 27 W and a 2 MB L2 cache.
>
> These CPUs should have PAE enabled. Only earlier versions of the Pentium M
> ( Older Dothans and the Banias core) do not have PAE support, officially.
>
> -Dennis.

Good point, patch updated to not show the warning if PAE is already
enabled.

Signed-off-by: Chris Bainbridge <chris.bainbridge@gmail.com>
---
diff --git a/arch/x86/boot/cpucheck.c b/arch/x86/boot/cpucheck.c
index 4d3ff03..3fd12bc 100644
--- a/arch/x86/boot/cpucheck.c
+++ b/arch/x86/boot/cpucheck.c
@@ -69,6 +69,13 @@ 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');
+}
+
static int has_fpu(void)
{
u16 fcw = -1, fsw = -1;
@@ -239,6 +246,21 @@ 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_flags();
+ } 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_flags();
+ }
+ else {
+ puts("Pentium M: PAE is disabled, "
+ "enable it with kernel argument \"forcepae\"\n"
+ "(this will taint the kernel)\n");
+ }
}

if (err_flags_ptr)
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index bbe1b8b..873cf3b 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -196,6 +196,14 @@ 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;
@@ -226,6 +234,15 @@ static void intel_workarounds(struct cpuinfo_x86 *c)
clear_cpu_cap(c, X86_FEATURE_SEP);

/*
+ * PAE CPUID bug: Pentium M reports no PAE but has PAE
+ */
+ 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.
*/

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