[patch V2 2/8] x86/smp: Dont access non-existing CPUID leaf

[Thomas Gleixner]

From: Tony Battersby <tonyb@xxxxxxxxxxxxxxx>

stop_this_cpu() tests CPUID leaf 0x8000001f::EAX unconditionally. CPUs
return the content of the highest supported leaf when a non-existing leaf
is read. So the result of the test is lottery except on AMD CPUs which
support that leaf.

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@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/3817d810-e0f1-8ef8-0bbd-663b919ca49b@xxxxxxxxxxxxxxx
---
 arch/x86/kernel/process.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -763,13 +763,15 @@ atomic_t stop_cpus_count;
 
 void __noreturn stop_this_cpu(void *dummy)
 {
+	struct cpuinfo_x86 *c = this_cpu_ptr(&cpu_info);
+
 	local_irq_disable();
 	/*
 	 * Remove this CPU:
 	 */
 	set_cpu_online(smp_processor_id(), 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
@@ -783,7 +785,7 @@ void __noreturn stop_this_cpu(void *dumm
 	 * 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();
 
 	/*