@@ -298,12 +298,19 @@ static void early_init_intel(struct cpuinfo_x86 *c)
clear_cpu_cap(c, X86_FEATURE_PAT);
/*
- * If fast string is not enabled in IA32_MISC_ENABLE for any reason,
- * clear the fast string and enhanced fast string CPU capabilities.
+ * Modern CPUs are generally expected to have a sane fast string
+ * implementation. However, BIOSes typically have a knob to tweak
+ * the architectural MISC_ENABLE.FAST_STRING enable bit.
+ *
+ * Adhere to the preference and program the linux-defined fast
+ * string flag and enhanced fast string capabilities accordingly.
*/
- if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
+ if (c->x86_vfm >= INTEL_PENTIUM_M_DOTHAN) {
rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
- if (!(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) {
+ if (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING) {
+ /* X86_FEATURE_ERMS is set based on CPUID */
+ set_cpu_cap(c, X86_FEATURE_REP_GOOD);
+ } else {
pr_info("Disabled fast string operations\n");
setup_clear_cpu_cap(X86_FEATURE_REP_GOOD);
setup_clear_cpu_cap(X86_FEATURE_ERMS);
@@ -554,8 +561,6 @@ static void init_intel(struct cpuinfo_x86 *c)
#ifdef CONFIG_X86_64
if (c->x86 == 15)
c->x86_cache_alignment = c->x86_clflush_size * 2;
- if (c->x86 == 6)
- set_cpu_cap(c, X86_FEATURE_REP_GOOD);
#else
/*
* Names for the Pentium II/Celeron processors
X86_FEATURE_REP_GOOD is a linux defined feature flag to track whether fast string operations should be used for copy_page(). It is also used as a second alternative for clear_page() if enhanced fast string operations (ERMS) are not available. X86_FEATURE_ERMS is an Intel-specific hardware-defined feature flag that tracks hardware support for Enhanced Fast strings. It is used to track whether Fast strings should be used for similar memory copy and memory clearing operations. On top of these, there is a FAST_STRING enable bit in the IA32_MISC_ENABLE MSR. It is typically controlled by the BIOS to provide a hint to the hardware and the OS on whether fast string operations are preferred. commit 161ec53c702c ("x86, mem, intel: Initialize Enhanced REP MOVSB/STOSB") introduced a mechanism to honor the BIOS preference for fast string operations and clear the above feature flags if needed. Unfortunately, the current initialization code for Intel to set and clear these bits is confusing at best and likely incorrect. X86_FEATURE_REP_GOOD is cleared in early_init_intel() if MISC_ENABLE.FAST_STRING is 0. But it gets set later on unconditionally for all Family 6 processors in init_intel(). This not only overrides the BIOS preference but also contradicts the earlier check. Fix this by combining the related checks and always relying on the BIOS provided preference for fast string operations. This simplification makes sure the upcoming Intel Family 18 and 19 models are covered as well. Signed-off-by: Sohil Mehta <sohil.mehta@intel.com> --- v3: Combine the REP_GOOD checks to one place. Improve code comments. v2: Separate out the REP_GOOD (copy page) specific change into a separate commit. --- arch/x86/kernel/cpu/intel.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-)