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

From: Andrew Cooper
Date: Wed Apr 01 2020 - 05:22:37 EST

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On 31/03/2020 23:53, Brian Gerst wrote:
> On Tue, Mar 31, 2020 at 6:44 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>> 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?
> Removing the warm_reset field from struct x86_legacy_features.

Ok, but that is still present as the 2nd hunk of the patch.

~Andrew

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