x86/bugs: Switch the selection of mitigation from CPU vendor to CPU features

Both AMD and Intel can have SPEC_CTRL_MSR for SSBD.

However AMD also has two more other ways of doing it - which
are !SPEC_CTRL MSR ways.

Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: [email protected]
Cc: KarimAllah Ahmed <[email protected]>
Cc: [email protected]
Cc: "H. Peter Anvin" <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: David Woodhouse <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: konradwilk

arch/x86/kernel/cpu/bugs.c

@@ -532,17 +532,12 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
 		 * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD may
 		 * use a completely different MSR and bit dependent on family.
 		 */
-		switch (boot_cpu_data.x86_vendor) {
-		case X86_VENDOR_INTEL:
-		case X86_VENDOR_AMD:
-			if (!static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) {
-				x86_amd_ssb_disable();
-				break;
-			}
+		if (!static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
+			x86_amd_ssb_disable();
+		else {
 			x86_spec_ctrl_base |= SPEC_CTRL_SSBD;
 			x86_spec_ctrl_mask |= SPEC_CTRL_SSBD;
 			wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
-			break;
 		}
 	}