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From:   Andrew Cooper <andrew.cooper3@citrix.com>
To:     LKML <linux-kernel@vger.kernel.org>
CC:     Andrew Cooper <andrew.cooper3@citrix.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, <x86@kernel.org>,
        "Jan Kiszka" <jan.kiszka@siemens.com>,
        James Morris <jmorris@namei.org>,
        "David Howells" <dhowells@redhat.com>,
        Matthew Garrett <mjg59@google.com>,
        Josh Boyer <jwboyer@redhat.com>,
        Steve Wahl <steve.wahl@hpe.com>,
        Mike Travis <mike.travis@hpe.com>,
        Dimitri Sivanich <dimitri.sivanich@hpe.com>,
        "Arnd Bergmann" <arnd@arndb.de>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Giovanni Gherdovich <ggherdovich@suse.cz>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Len Brown <len.brown@intel.com>,
        Kees Cook <keescook@chromium.org>,
        Martin Molnar <martin.molnar.programming@gmail.com>,
        Pingfan Liu <kernelfans@gmail.com>,
        <jailhouse-dev@googlegroups.com>
Subject: [PATCH v2] x86/smpboot: Remove 486-isms from the modern AP boot path
Date:   Tue, 31 Mar 2020 18:58:10 +0100
Message-ID: <20200331175810.30204-1-andrew.cooper3@citrix.com>
In-Reply-To: <20200325101431.12341-1-andrew.cooper3@citrix.com>
References: <20200325101431.12341-1-andrew.cooper3@citrix.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Linux has an implementation of the Universal Start-up Algorithm (MP spec,
Appendix B.4, Application Processor Startup), which includes unconditionally
writing to the Bios Data Area and CMOS registers.

The warm reset vector is only necessary in the non-integrated Local APIC case.
UV and Jailhouse already have an opt-out for this behaviour, but blindly using
the BDA and CMOS on a UEFI or other reduced hardware system isn't clever.

We could make this conditional on the integrated-ness of the Local APIC, but
486-era SMP isn't supported.  Drop the logic completely, tidying up the includ
list and header files as appropriate.

CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: Borislav Petkov <bp@alien8.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: x86@kernel.org
CC: Jan Kiszka <jan.kiszka@siemens.com>
CC: James Morris <jmorris@namei.org>
CC: David Howells <dhowells@redhat.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Matthew Garrett <mjg59@google.com>
CC: Josh Boyer <jwboyer@redhat.com>
CC: Steve Wahl <steve.wahl@hpe.com>
CC: Mike Travis <mike.travis@hpe.com>
CC: Dimitri Sivanich <dimitri.sivanich@hpe.com>
CC: Arnd Bergmann <arnd@arndb.de>
CC: "Peter Zijlstra (Intel)" <peterz@infradead.org>
CC: Giovanni Gherdovich <ggherdovich@suse.cz>
CC: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
CC: Len Brown <len.brown@intel.com>
CC: Kees Cook <keescook@chromium.org>
CC: Martin Molnar <martin.molnar.programming@gmail.com>
CC: Pingfan Liu <kernelfans@gmail.com>
CC: linux-kernel@vger.kernel.org
CC: jailhouse-dev@googlegroups.com
Suggested-by: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
v2:
 * Drop logic entirely, rather than retaining support in 32bit builds.
---
 arch/x86/include/asm/apic.h        |  6 -----
 arch/x86/include/asm/x86_init.h    |  1 -
 arch/x86/kernel/apic/x2apic_uv_x.c |  1 -
 arch/x86/kernel/jailhouse.c        |  1 -
 arch/x86/kernel/platform-quirks.c  |  1 -
 arch/x86/kernel/smpboot.c          | 50 --------------------------------------
 6 files changed, 60 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 19e94af9cc5d..5c33f9374b28 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -472,12 +472,6 @@ static inline unsigned default_get_apic_id(unsigned long x)
 		return (x >> 24) & 0x0F;
 }
 
-/*
- * Warm reset vector position:
- */
-#define TRAMPOLINE_PHYS_LOW		0x467
-#define TRAMPOLINE_PHYS_HIGH		0x469
-
 extern void generic_bigsmp_probe(void);
 
 #ifdef CONFIG_X86_LOCAL_APIC
diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index 96d9cd208610..006a5d7fd7eb 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -229,7 +229,6 @@ enum x86_legacy_i8042_state {
 struct x86_legacy_features {
 	enum x86_legacy_i8042_state i8042;
 	int rtc;
-	int warm_reset;
 	int no_vga;
 	int reserve_bios_regions;
 	struct x86_legacy_devices devices;
diff --git a/arch/x86/kernel/apic/x2apic_uv_x.c b/arch/x86/kernel/apic/x2apic_uv_x.c
index ad53b2abc859..5afcfd193592 100644
--- a/arch/x86/kernel/apic/x2apic_uv_x.c
+++ b/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -343,7 +343,6 @@ static int __init uv_acpi_madt_oem_check(char *_oem_id, char *_oem_table_id)
 	} else if (!strcmp(oem_table_id, "UVH")) {
 		/* Only UV1 systems: */
 		uv_system_type = UV_NON_UNIQUE_APIC;
-		x86_platform.legacy.warm_reset = 0;
 		__this_cpu_write(x2apic_extra_bits, pnodeid << uvh_apicid.s.pnode_shift);
 		uv_set_apicid_hibit();
 		uv_apic = 1;
diff --git a/arch/x86/kernel/jailhouse.c b/arch/x86/kernel/jailhouse.c
index 6eb8b50ea07e..d628fe92d6af 100644
--- a/arch/x86/kernel/jailhouse.c
+++ b/arch/x86/kernel/jailhouse.c
@@ -210,7 +210,6 @@ static void __init jailhouse_init_platform(void)
 	x86_platform.calibrate_tsc	= jailhouse_get_tsc;
 	x86_platform.get_wallclock	= jailhouse_get_wallclock;
 	x86_platform.legacy.rtc		= 0;
-	x86_platform.legacy.warm_reset	= 0;
 	x86_platform.legacy.i8042	= X86_LEGACY_I8042_PLATFORM_ABSENT;
 
 	legacy_pic			= &null_legacy_pic;
diff --git a/arch/x86/kernel/platform-quirks.c b/arch/x86/kernel/platform-quirks.c
index b348a672f71d..d922c5e0c678 100644
--- a/arch/x86/kernel/platform-quirks.c
+++ b/arch/x86/kernel/platform-quirks.c
@@ -9,7 +9,6 @@ void __init x86_early_init_platform_quirks(void)
 {
 	x86_platform.legacy.i8042 = X86_LEGACY_I8042_EXPECTED_PRESENT;
 	x86_platform.legacy.rtc = 1;
-	x86_platform.legacy.warm_reset = 1;
 	x86_platform.legacy.reserve_bios_regions = 0;
 	x86_platform.legacy.devices.pnpbios = 1;
 
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index fe3ab9632f3b..a9f5b511d0b4 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -72,7 +72,6 @@
 #include <asm/fpu/internal.h>
 #include <asm/setup.h>
 #include <asm/uv/uv.h>
-#include <linux/mc146818rtc.h>
 #include <asm/i8259.h>
 #include <asm/misc.h>
 #include <asm/qspinlock.h>
@@ -119,34 +118,6 @@ int arch_update_cpu_topology(void)
 	return retval;
 }
 
-static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&rtc_lock, flags);
-	CMOS_WRITE(0xa, 0xf);
-	spin_unlock_irqrestore(&rtc_lock, flags);
-	*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_HIGH)) =
-							start_eip >> 4;
-	*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) =
-							start_eip & 0xf;
-}
-
-static inline void smpboot_restore_warm_reset_vector(void)
-{
-	unsigned long flags;
-
-	/*
-	 * Paranoid:  Set warm reset code and vector here back
-	 * to default values.
-	 */
-	spin_lock_irqsave(&rtc_lock, flags);
-	CMOS_WRITE(0, 0xf);
-	spin_unlock_irqrestore(&rtc_lock, flags);
-
-	*((volatile u32 *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = 0;
-}
-
 static void init_freq_invariance(void);
 
 /*
@@ -1049,20 +1020,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,
 	 * the targeted processor.
 	 */
 
-	if (x86_platform.legacy.warm_reset) {
-
-		pr_debug("Setting warm reset code and vector.\n");
-
-		smpboot_setup_warm_reset_vector(start_ip);
-		/*
-		 * Be paranoid about clearing APIC errors.
-		*/
-		if (APIC_INTEGRATED(boot_cpu_apic_version)) {
-			apic_write(APIC_ESR, 0);
-			apic_read(APIC_ESR);
-		}
-	}
-
 	/*
 	 * AP might wait on cpu_callout_mask in cpu_init() with
 	 * cpu_initialized_mask set if previous attempt to online
@@ -1118,13 +1075,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,
 		}
 	}
 
-	if (x86_platform.legacy.warm_reset) {
-		/*
-		 * Cleanup possible dangling ends...
-		 */
-		smpboot_restore_warm_reset_vector();
-	}
-
 	return boot_error;
 }
 
-- 
2.11.0