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

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

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.

~Andrew