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

    --
    Brian Gerst

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