linux-kernel - [PATCH] Use x2apic enabled bit as set by BIOS to indicate APIC mode

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Date:   Thu,  8 Apr 2021 11:00:47 -0500
From:   Mike Travis <mike.travis@....com>
To:     Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steve Wahl <steve.wahl@....com>, x86@...nel.org
Cc:     Mike Travis <mike.travis@....com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Russ Anderson <russ.anderson@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] Use x2apic enabled bit as set by BIOS to indicate APIC mode

BIOS now sets the x2apic enabled bit (and the ACPI table) for extended
APIC modes.  Use that bit to indicate if extended mode is set.

Signed-off-by: Mike Travis <mike.travis@....com>
---
 arch/x86/kernel/apic/x2apic_uv_x.c | 31 ++++++++++++++----------------
 1 file changed, 14 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/apic/x2apic_uv_x.c b/arch/x86/kernel/apic/x2apic_uv_x.c
index 52bc217ca8c3..2e99605f9a05 100644
--- a/arch/x86/kernel/apic/x2apic_uv_x.c
+++ b/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -369,6 +369,15 @@ static int __init early_get_arch_type(void)
 	return ret;
 }
 
+/* UV system found, check which APIC MODE BIOS already selected */
+static void __init early_set_apic_mode(void)
+{
+	if (x2apic_enabled())
+		uv_system_type = UV_X2APIC;
+	else
+		uv_system_type = UV_LEGACY_APIC;
+}
+
 static int __init uv_set_system_type(char *_oem_id, char *_oem_table_id)
 {
 	/* Save OEM_ID passed from ACPI MADT */
@@ -404,11 +413,13 @@ static int __init uv_set_system_type(char *_oem_id, char *_oem_table_id)
 		else
 			uv_hubless_system |= 0x8;
 
-		/* Copy APIC type */
+		/* Copy OEM Table ID and set APIC Mode */
 		uv_stringify(sizeof(oem_table_id), oem_table_id, _oem_table_id);
+		early_set_apic_mode();
 
 		pr_info("UV: OEM IDs %s/%s, SystemType %d, HUBLESS ID %x\n",
 			oem_id, oem_table_id, uv_system_type, uv_hubless_system);
+
 		return 0;
 	}
 
@@ -453,6 +464,7 @@ static int __init uv_set_system_type(char *_oem_id, char *_oem_table_id)
 	early_set_hub_type();
 
 	/* Other UV setup functions */
+	early_set_apic_mode();
 	early_get_pnodeid();
 	early_get_apic_socketid_shift();
 	x86_platform.is_untracked_pat_range = uv_is_untracked_pat_range;
@@ -472,29 +484,14 @@ static int __init uv_acpi_madt_oem_check(char *_oem_id, char *_oem_table_id)
 	if (uv_set_system_type(_oem_id, _oem_table_id) == 0)
 		return 0;
 
-	/* Save and Decode OEM Table ID */
+	/* Save for display of the OEM Table ID */
 	uv_stringify(sizeof(oem_table_id), oem_table_id, _oem_table_id);
 
-	/* This is the most common hardware variant, x2apic mode */
-	if (!strcmp(oem_table_id, "UVX"))
-		uv_system_type = UV_X2APIC;
-
-	/* Only used for very small systems, usually 1 chassis, legacy mode  */
-	else if (!strcmp(oem_table_id, "UVL"))
-		uv_system_type = UV_LEGACY_APIC;
-
-	else
-		goto badbios;
-
 	pr_info("UV: OEM IDs %s/%s, System/UVType %d/0x%x, HUB RevID %d\n",
 		oem_id, oem_table_id, uv_system_type, is_uv(UV_ANY),
 		uv_min_hub_revision_id);
 
 	return 0;
-
-badbios:
-	pr_err("UV: UVarchtype:%s not supported\n", uv_archtype);
-	BUG();
 }
 
 enum uv_system_type get_uv_system_type(void)
-- 
2.21.0