[tip:x86/cpu] x86/cpu/amd: Set X86_FEATURE_EXTD_APICID for future processors

[tip-bot for Aravind Gopalakrishnan]

Commit-ID:  b9d16a2a21aa9c264a29dd84d6f7b03581517a03
Gitweb:     http://git.kernel.org/tip/b9d16a2a21aa9c264a29dd84d6f7b03581517a03
Author:     Aravind Gopalakrishnan <Aravind.Gopalakrishnan@xxxxxxx>
AuthorDate: Mon, 27 Apr 2015 10:25:51 -0500
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 6 May 2015 11:16:53 +0200

x86/cpu/amd: Set X86_FEATURE_EXTD_APICID for future processors

Decision to use a 4-bit mask or 8-bit mask in default_get_apic_id()
is controlled by setting capability bit X86_FEATURE_EXTD_APICID.

Currently, we detect extended APIC ID support by accessing Link
Transaction Control register D18F0x68 in PCI config space.

But, not even that is needed as we can safely postulate that future
AMD processors will support 8-bit APIC IDs and we can simply set that
feature bit on them, without the PCI access.

Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@xxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Jacob Shin <jacob.w.shin@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: dave.hansen@xxxxxxxxxxxxxxx
Cc: hecmargi@xxxxxx
Cc: mgorman@xxxxxxx
Link: http://lkml.kernel.org/r/1430148351-9013-1-git-send-email-Aravind.Gopalakrishnan@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/cpu/amd.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index e4cf633..94e7051 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -520,8 +520,16 @@ static void early_init_amd(struct cpuinfo_x86 *c)
 			set_cpu_cap(c, X86_FEATURE_K6_MTRR);
 #endif
 #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_PCI)
-	/* check CPU config space for extended APIC ID */
-	if (cpu_has_apic && c->x86 >= 0xf) {
+	/*
+	 * ApicID can always be treated as an 8-bit value for AMD APIC versions
+	 * >= 0x10, but even old K8s came out of reset with version 0x10. So, we
+	 * can safely set X86_FEATURE_EXTD_APICID unconditionally for families
+	 * after 16h.
+	 */
+	if (cpu_has_apic && c->x86 > 0x16) {
+		set_cpu_cap(c, X86_FEATURE_EXTD_APICID);
+	} else if (cpu_has_apic && c->x86 >= 0xf) {
+		/* check CPU config space for extended APIC ID */
 		unsigned int val;
 		val = read_pci_config(0, 24, 0, 0x68);
 		if ((val & ((1 << 17) | (1 << 18))) == ((1 << 17) | (1 << 18)))
--
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