From: Andrew Lutomirski <l...@mit.edu> Intel SDM volume 3A, 8.4.2 says:
Software can disable fast-string operation by clearing the fast-string-enable bit (bit 0) of IA32_MISC_ENABLE MSR. However, Intel recomments that system software always enable fast-string operation. The Intel DQ67SW board (with latest BIOS) disables fast string operations if TXT is enabled. A Lenovo X220 disables it regardless of TXT setting. I doubt I'm the only person with a dumb BIOS like this. Signed-off-by: Andy Lutomirski <l...@amacapital.net> --- v4 was a almost two years ago, but I just noticed that this is still a problem. This is tested on v3.9. https://patchwork.kernel.org/patch/1073972/ This is identical to v4 of this patch except that it uses wrmsrl_safe instead of wrmsr_safe. arch/x86/kernel/cpu/intel.c | 27 ++++++++++++++++++++++----- 1 file changed, 22 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index 1905ce9..a4a3ef2 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -29,6 +29,7 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c) { u64 misc_enable; + bool allow_fast_string = true; /* Unmask CPUID levels if masked: */ if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) { @@ -119,10 +120,11 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c) * (model 2) with the same problem. */ if (c->x86 == 15) { - rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable); + allow_fast_string = false; + rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable); if (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING) { - printk(KERN_INFO "kmemcheck: Disabling fast string operations\n"); + printk_once(KERN_INFO "kmemcheck: Disabling fast string operations\n"); misc_enable &= ~MSR_IA32_MISC_ENABLE_FAST_STRING; wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable); @@ -131,13 +133,28 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c) #endif /* - * If fast string is not enabled in IA32_MISC_ENABLE for any reason, - * clear the fast string and enhanced fast string CPU capabilities. + * If BIOS didn't enable fast string operation, try to enable + * it ourselves. If that fails, then clear the fast string + * and enhanced fast string CPU capabilities. */ if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) { rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable); + + if (allow_fast_string && + !(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) { + misc_enable |= MSR_IA32_MISC_ENABLE_FAST_STRING; + wrmsrl_safe(MSR_IA32_MISC_ENABLE, misc_enable); + + /* Re-read to make sure it stuck. */ + rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable); + + if (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING) + printk_once(KERN_INFO FW_WARN "IA32_MISC_ENABLE.FAST_STRING_ENABLE was not set\n"); + } + if (!(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) { - printk(KERN_INFO "Disabled fast string operations\n"); + if (allow_fast_string) + printk_once(KERN_INFO "Failed to enable fast string operations\n"); setup_clear_cpu_cap(X86_FEATURE_REP_GOOD); setup_clear_cpu_cap(X86_FEATURE_ERMS); } -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
