[PATCH v2 4/8] x86/pti: Do not enable PTI on fixed Intel processors

[David Woodhouse <dwmw@amazon.co.uk>]

When they advertise the IA32_ARCH_CAPABILITIES MSR and it has the RDCL_NO
bit set, they don't need KPTI either.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 arch/x86/kernel/cpu/common.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index e5d66e9..80572ae 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -900,8 +900,13 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 
 	setup_force_cpu_cap(X86_FEATURE_ALWAYS);
 
-	if (c->x86_vendor != X86_VENDOR_AMD)
-		setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN);
+	if (c->x86_vendor != X86_VENDOR_AMD) {
+		unsigned long ia32_cap = 0;
+		if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES))
+			rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
+		if (!(ia32_cap & ARCH_CAP_RDCL_NO))
+			setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN);
+	}
 
 	setup_force_cpu_bug(X86_BUG_SPECTRE_V1);
 	setup_force_cpu_bug(X86_BUG_SPECTRE_V2);
-- 
2.7.4