Merge: cpufreq: intel_pstate: Unchecked MSR aceess in legacy mode

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-10/-/merge_requests/861

JIRA: https://issues.redhat.com/browse/RHEL-81034

Build Info: 67517444

commit ac4e04d
Author: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Date:   Tue Apr 29 14:07:11 2025 -0700

    cpufreq: intel_pstate: Unchecked MSR aceess in legacy mode

    When turbo mode is unavailable on a Skylake-X system, executing the
    command:

    results in an unchecked MSR access error:

     WRMSR to 0x199 (attempted to write 0x0000000100001300).

    This issue was reproduced on an OEM (Original Equipment Manufacturer)
    system and is not a common problem across all Skylake-X systems.

    This error occurs because the MSR 0x199 Turbo Engage Bit (bit 32) is set
    when turbo mode is disabled. The issue arises when intel_pstate fails to
    detect that turbo mode is disabled. Here intel_pstate relies on
    MSR_IA32_MISC_ENABLE bit 38 to determine the status of turbo mode.
    However, on this system, bit 38 is not set even when turbo mode is
    disabled.

    According to the Intel Software Developer's Manual (SDM), the BIOS sets
    this bit during platform initialization to enable or disable
    opportunistic processor performance operations. Logically, this bit
    should be set in such cases. However, the SDM also specifies that "OS
    and applications must use CPUID leaf 06H to detect processors with
    opportunistic processor performance operations enabled."

    Therefore, in addition to checking MSR_IA32_MISC_ENABLE bit 38, verify
    that CPUID.06H:EAX[1] is 0 to accurately determine if turbo mode is
    disabled.

    Fixes: 4521e1a ("cpufreq: intel_pstate: Reflect current no_turbo state correctly")
    Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
    Cc: All applicable <stable@vger.kernel.org>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Signed-off-by: Steve Best <sbest@redhat.com>

Approved-by: Tony Camuso <tcamuso@redhat.com>

Merged-by: Julio Faracco <jfaracco@redhat.com>

Author: jcfaracco

drivers/cpufreq/intel_pstate.c

@@ -598,6 +598,9 @@ static bool turbo_is_disabled(void)
 {
 	u64 misc_en;
 
+	if (!cpu_feature_enabled(X86_FEATURE_IDA))
+		return true;
+
 	rdmsrl(MSR_IA32_MISC_ENABLE, misc_en);
 
 	return !!(misc_en & MSR_IA32_MISC_ENABLE_TURBO_DISABLE);