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

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 01/04/2020 12:39, Brian Gerst wrote:
> On Wed, Apr 1, 2020 at 5:22 AM Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>> On 31/03/2020 23:53, Brian Gerst wrote:
>>> On Tue, Mar 31, 2020 at 6:44 PM Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>>>> On 31/03/2020 23:23, Brian Gerst wrote:
>>>>> On Tue, Mar 31, 2020 at 1:59 PM Andrew Cooper <andrew.cooper3@citrix.com> 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@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;
>>>>>>  }
>>>>> 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.
> My apologies, Gmail was hiding that section of the patch because it
> was a reply to the original patch.  For future reference, add the
> version number to the title when resubmitting a patch (ie. [PATCH
> v2]).

Erm... is Gmail hiding that too?

Lore thinks it is there:
https://lore.kernel.org/lkml/CAMzpN2g0LS5anGc7CXco4pgBHhGzc8hw+shMOg8WEWGsx+BHpg@mail.gmail.com/

~Andrew