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SubjectRE: [PATCH v2 1/2] x86: Enable fast strings on Intel if BIOS hasn't already
> -----Original Message-----
> From: Andy Lutomirski [mailto:luto@MIT.EDU]
> Sent: Saturday, August 06, 2011 4:43 AM
> To: x86@kernel.org; linux-kernel@vger.kernel.org
> Cc: Yu, Fenghua; Matthew Garrett; Len Brown; linux-
> acpi@vger.kernel.org; Ingo Molnar; Andy Lutomirski
> Subject: [PATCH v2 1/2] x86: Enable fast strings on Intel if BIOS
> hasn't already
>
> 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 <luto@mit.edu>
> ---
> arch/x86/kernel/cpu/intel.c | 25 ++++++++++++++++++++++---
> 1 files changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index ed6086e..c80ab41 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -30,6 +30,7 @@
> 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)) {
> @@ -118,8 +119,9 @@ 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");
>
> @@ -130,11 +132,28 @@ 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;
> + wrmsr_safe(MSR_IA32_MISC_ENABLE, (u32)misc_enable,
> + (u32)(misc_enable >> 32));
> +
> + /* Re-read to make sure it stuck. */
> + rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
> +
> + if (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)
> + printk(KERN_WARNING FW_WARN "CPU #%d: "
> + "IA32_MISC_ENABLE.FAST_STRING_ENABLE "
> + "was not set", c->cpu_index);
This printk is redundant because the same info is dumped in the below printk. Plus it's not firmware's issue if we can not set fast string bit 0 in MISC_ENABLE register. So I don't think FW_WARN is right.

I would suggest to remove this printk (and the if () statement) and change KERN_INFO to KERN_WARNING in the following printk.
> + }
> +
> if (!(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) {
> printk(KERN_INFO "Disabled fast string
> operations\n");
> setup_clear_cpu_cap(X86_FEATURE_REP_GOOD);
> --
> 1.7.6



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