Re: [PATCH v2] x86/smpboot: Remove 486-isms from the modern AP boot path

From: Andrew Cooper
Date: Tue Mar 31 2020 - 18:45:00 EST

On 31/03/2020 23:23, Brian Gerst wrote:
> On Tue, Mar 31, 2020 at 1:59 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>> 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@xxxxxxxxxxxxx>
>> CC: Ingo Molnar <mingo@xxxxxxxxxx>
>> CC: Borislav Petkov <bp@xxxxxxxxx>
>> CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
>> CC: x86@xxxxxxxxxx
>> CC: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
>> CC: James Morris <jmorris@xxxxxxxxx>
>> CC: David Howells <dhowells@xxxxxxxxxx>
>> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> CC: Matthew Garrett <mjg59@xxxxxxxxxx>
>> CC: Josh Boyer <jwboyer@xxxxxxxxxx>
>> CC: Steve Wahl <steve.wahl@xxxxxxx>
>> CC: Mike Travis <mike.travis@xxxxxxx>
>> CC: Dimitri Sivanich <dimitri.sivanich@xxxxxxx>
>> CC: Arnd Bergmann <arnd@xxxxxxxx>
>> CC: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>
>> CC: Giovanni Gherdovich <ggherdovich@xxxxxxx>
>> CC: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
>> CC: Len Brown <len.brown@xxxxxxxxx>
>> CC: Kees Cook <keescook@xxxxxxxxxxxx>
>> CC: Martin Molnar <martin.molnar.programming@xxxxxxxxx>
>> CC: Pingfan Liu <kernelfans@xxxxxxxxx>
>> CC: linux-kernel@xxxxxxxxxxxxxxx
>> CC: jailhouse-dev@xxxxxxxxxxxxxxxx
>> Suggested-by: "H. Peter Anvin" <hpa@xxxxxxxxx>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> 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;
>> }
> You removed x86_platform.legacy.warm_reset in the original patch, but
> that is missing in V2.

Second hunk? Or are you referring to something different?

~Andrew