x86/smp: Dont access non-existing CPUID leaf

stop_this_cpu() tests CPUID leaf 0x8000001f::EAX unconditionally. Intel
CPUs return the content of the highest supported leaf when a non-existing
leaf is read, while AMD CPUs return all zeros for unsupported leafs.

So the result of the test on Intel CPUs is lottery.

While harmless it's incorrect and causes the conditional wbinvd() to be
issued where not required.

Check whether the leaf is supported before reading it.

[ tglx: Adjusted changelog ]

Fixes: 08f253ec3767 ("x86/cpu: Clear SME feature flag when not in use")
Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/3817d810-e0f1-8ef8-0bbd-663b919ca49b@cybernetics.com
Link: https://lore.kernel.org/r/20230615193330.322186388@linutronix.de

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 05924bc4b3af21ac7c346037008169e63689c658..ff9b80a0e3e3bc7f86f02b3c459d96e133f815e7 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -763,6 +763,7 @@ struct cpumask cpus_stop_mask;
 
 void __noreturn stop_this_cpu(void *dummy)
 {
+       struct cpuinfo_x86 *c = this_cpu_ptr(&cpu_info);
        unsigned int cpu = smp_processor_id();
 
        local_irq_disable();
@@ -777,7 +778,7 @@ void __noreturn stop_this_cpu(void *dummy)
         */
        set_cpu_online(cpu, false);
        disable_local_APIC();
-       mcheck_cpu_clear(this_cpu_ptr(&cpu_info));
+       mcheck_cpu_clear(c);
 
        /*
         * Use wbinvd on processors that support SME. This provides support
@@ -791,7 +792,7 @@ void __noreturn stop_this_cpu(void *dummy)
         * Test the CPUID bit directly because the machine might've cleared
         * X86_FEATURE_SME due to cmdline options.
         */
-       if (cpuid_eax(0x8000001f) & BIT(0))
+       if (c->extended_cpuid_level >= 0x8000001f && (cpuid_eax(0x8000001f) & BIT(0)))
                native_wbinvd();
 
        /*