* Andy Lutomirski <[email protected]> wrote: > From: Andrew Lutomirski <[email protected]> > > 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.
Hm, I think we could try this. Do we know whether Windows enables it? Most laptop vendors will test/certify on Windows, so that's the 'expected' environment. > Signed-off-by: Andy Lutomirski <[email protected]> > --- > > 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); I think we should also printk if we enabled it against the BIOS setting - so that if the user sees any problems it can possibly be tracked back to this change ... I.e. stay silent if the BIOS has it enabled already - but otherwise document our action. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
