| Message ID | 20230414232311.379210081@linutronix.de (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | cpu/hotplug, x86: Reworked parallel CPU bringup | expand |
On Fri, Apr 14, 2023 at 7:45 PM Thomas Gleixner <tglx@linutronix.de> wrote: > > From: David Woodhouse <dwmw@amazon.co.uk> > > Rework the real-mode startup code to allow for APs to be brought up in > parallel. This is in two parts: > > 1. Introduce a bit-spinlock to prevent them from all using the real > mode stack at the same time. > > 2. Avoid needing to use the global smpboot_control variable to pass > each AP its CPU number. > > To achieve the latter, export the cpuid_to_apicid[] array so that each > AP can find its own CPU number by searching therein based on its APIC ID. > > Introduce flags in the top bits of smpboot_control which indicate methods > by which an AP should find its CPU number. For a serialized bringup, the > CPU number is explicitly passed in the low bits of smpboot_control as > before. For parallel mode there are flags directing the AP to find its APIC > ID in CPUID leaf 0x0b or 1x1f (for X2APIC mode) or CPUID leaf 0x01 where 8 > bits are sufficient, then perform the cpuid_to_apicid[] lookup with that. > > Aside from the fact that APs will now look up their CPU number via the > newly-exported cpuid_to_apicid[] table, there is no behavioural change > intended, since the parallel bootup has not yet been enabled. > > [ tglx: Initial proof of concept patch with bitlock and APIC ID lookup ] > [ dwmw2: Rework and testing, commit message, CPUID 0x1 and CPU0 support ] > [ seanc: Fix stray override of initial_gs in common_cpu_up() ] > [ Oleksandr Natalenko: reported suspend/resume issue fixed in > x86_acpi_suspend_lowlevel ] > > Co-developed-by: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > Co-developed-by: Brian Gerst <brgerst@gmail.com> > Signed-off-by: Brian Gerst <brgerst@gmail.com> > Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> > Signed-off-by: Usama Arif <usama.arif@bytedance.com> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > --- > arch/x86/include/asm/apic.h | 2 > arch/x86/include/asm/realmode.h | 3 + > arch/x86/include/asm/smp.h | 8 +++ > arch/x86/kernel/acpi/sleep.c | 9 +++ > arch/x86/kernel/apic/apic.c | 2 > arch/x86/kernel/head_64.S | 79 ++++++++++++++++++++++++++++++++++- > arch/x86/kernel/smpboot.c | 5 -- > arch/x86/realmode/init.c | 3 + > arch/x86/realmode/rm/trampoline_64.S | 27 +++++++++-- > 9 files changed, 125 insertions(+), 13 deletions(-) > > --- a/arch/x86/include/asm/apic.h > +++ b/arch/x86/include/asm/apic.h > @@ -55,6 +55,8 @@ extern int local_apic_timer_c2_ok; > extern int disable_apic; > extern unsigned int lapic_timer_period; > > +extern int cpuid_to_apicid[]; > + > extern enum apic_intr_mode_id apic_intr_mode; > enum apic_intr_mode_id { > APIC_PIC, > --- a/arch/x86/include/asm/realmode.h > +++ b/arch/x86/include/asm/realmode.h > @@ -52,6 +52,7 @@ struct trampoline_header { > u64 efer; > u32 cr4; > u32 flags; > + u32 lock; > #endif > }; > > @@ -64,6 +65,8 @@ extern unsigned long initial_stack; > extern unsigned long initial_vc_handler; > #endif > > +extern u32 *trampoline_lock; > + > extern unsigned char real_mode_blob[]; > extern unsigned char real_mode_relocs[]; > > --- a/arch/x86/include/asm/smp.h > +++ b/arch/x86/include/asm/smp.h > @@ -198,4 +198,12 @@ extern unsigned int smpboot_control; > > #endif /* !__ASSEMBLY__ */ > > +/* Control bits for startup_64 */ > +#define STARTUP_APICID_CPUID_1F 0x80000000 > +#define STARTUP_APICID_CPUID_0B 0x40000000 > +#define STARTUP_APICID_CPUID_01 0x20000000 > + > +/* Top 8 bits are reserved for control */ > +#define STARTUP_PARALLEL_MASK 0xFF000000 > + > #endif /* _ASM_X86_SMP_H */ > --- a/arch/x86/kernel/acpi/sleep.c > +++ b/arch/x86/kernel/acpi/sleep.c > @@ -16,6 +16,7 @@ > #include <asm/cacheflush.h> > #include <asm/realmode.h> > #include <asm/hypervisor.h> > +#include <asm/smp.h> > > #include <linux/ftrace.h> > #include "../../realmode/rm/wakeup.h" > @@ -127,7 +128,13 @@ int x86_acpi_suspend_lowlevel(void) > * value is in the actual %rsp register. > */ > current->thread.sp = (unsigned long)temp_stack + sizeof(temp_stack); > - smpboot_control = smp_processor_id(); > + /* > + * Ensure the CPU knows which one it is when it comes back, if > + * it isn't in parallel mode and expected to work that out for > + * itself. > + */ > + if (!(smpboot_control & STARTUP_PARALLEL_MASK)) > + smpboot_control = smp_processor_id(); > #endif > initial_code = (unsigned long)wakeup_long64; > saved_magic = 0x123456789abcdef0L; > --- a/arch/x86/kernel/apic/apic.c > +++ b/arch/x86/kernel/apic/apic.c > @@ -2377,7 +2377,7 @@ static int nr_logical_cpuids = 1; > /* > * Used to store mapping between logical CPU IDs and APIC IDs. > */ > -static int cpuid_to_apicid[] = { > +int cpuid_to_apicid[] = { > [0 ... NR_CPUS - 1] = -1, > }; > > --- a/arch/x86/kernel/head_64.S > +++ b/arch/x86/kernel/head_64.S > @@ -25,6 +25,7 @@ > #include <asm/export.h> > #include <asm/nospec-branch.h> > #include <asm/fixmap.h> > +#include <asm/smp.h> > > /* > * We are not able to switch in one step to the final KERNEL ADDRESS SPACE > @@ -234,8 +235,70 @@ SYM_INNER_LABEL(secondary_startup_64_no_ > ANNOTATE_NOENDBR // above > > #ifdef CONFIG_SMP > + /* > + * For parallel boot, the APIC ID is retrieved from CPUID, and then > + * used to look up the CPU number. For booting a single CPU, the > + * CPU number is encoded in smpboot_control. > + * > + * Bit 31 STARTUP_APICID_CPUID_1F flag (use CPUID 0x1f) > + * Bit 30 STARTUP_APICID_CPUID_0B flag (use CPUID 0x0b) > + * Bit 29 STARTUP_APICID_CPUID_01 flag (use CPUID 0x01) > + * Bit 0-23 CPU# if STARTUP_APICID_CPUID_xx flags are not set > + */ > movl smpboot_control(%rip), %ecx > + testl $STARTUP_APICID_CPUID_1F, %ecx > + jnz .Luse_cpuid_1f > + testl $STARTUP_APICID_CPUID_0B, %ecx > + jnz .Luse_cpuid_0b > + testl $STARTUP_APICID_CPUID_01, %ecx > + jnz .Luse_cpuid_01 > + andl $(~STARTUP_PARALLEL_MASK), %ecx > + jmp .Lsetup_cpu > + > +.Luse_cpuid_01: > + mov $0x01, %eax > + cpuid > + mov %ebx, %edx > + shr $24, %edx > + jmp .Lsetup_AP > + > +.Luse_cpuid_0b: > + mov $0x0B, %eax > + xorl %ecx, %ecx > + cpuid > + jmp .Lsetup_AP > + > +.Luse_cpuid_1f: > + mov $0x1f, %eax > + xorl %ecx, %ecx > + cpuid > > +.Lsetup_AP: > + /* EDX contains the APIC ID of the current CPU */ > + xorq %rcx, %rcx > + leaq cpuid_to_apicid(%rip), %rbx > + > +.Lfind_cpunr: > + cmpl (%rbx,%rcx,4), %edx > + jz .Lsetup_cpu > + inc %ecx > +#ifdef CONFIG_FORCE_NR_CPUS > + cmpl $NR_CPUS, %ecx > +#else > + cmpl nr_cpu_ids(%rip), %ecx > +#endif > + jb .Lfind_cpunr > + > + /* APIC ID not found in the table. Drop the trampoline lock and bail. */ > + movq trampoline_lock(%rip), %rax > + lock > + btrl $0, (%rax) > + > +1: cli > + hlt > + jmp 1b > + > +.Lsetup_cpu: > /* Get the per cpu offset for the given CPU# which is in ECX */ > movq __per_cpu_offset(,%rcx,8), %rdx > #else > @@ -248,10 +311,20 @@ SYM_INNER_LABEL(secondary_startup_64_no_ > * > * RDX contains the per-cpu offset > */ > - movq pcpu_hot + X86_current_task(%rdx), %rax > - movq TASK_threadsp(%rax), %rsp > + movq pcpu_hot + X86_top_of_stack(%rdx), %rsp Switching to using pcpu_hot.top_of_stack is ok, but it's not completely equivalent. top_of_stack points to the end of the pt_regs structure, while the kernel stack starts below pt_regs even for kernel threads. So you need to subtract PTREGS_SIZE from the stack pointer after this. This change should also be a separate patch. -- Brian Gerst
On Sat, Apr 15 2023 at 09:22, Brian Gerst wrote: > On Fri, Apr 14, 2023 at 7:45 PM Thomas Gleixner <tglx@linutronix.de> wrote: >> @@ -248,10 +311,20 @@ SYM_INNER_LABEL(secondary_startup_64_no_ >> * >> * RDX contains the per-cpu offset >> */ >> - movq pcpu_hot + X86_current_task(%rdx), %rax >> - movq TASK_threadsp(%rax), %rsp >> + movq pcpu_hot + X86_top_of_stack(%rdx), %rsp > > Switching to using pcpu_hot.top_of_stack is ok, but it's not > completely equivalent. top_of_stack points to the end of the pt_regs > structure, while the kernel stack starts below pt_regs even for kernel > threads. So you need to subtract PTREGS_SIZE from the stack pointer > after this. > > This change should also be a separate patch. You're right on both counts.
On Sat, Apr 15 2023 at 23:06, Thomas Gleixner wrote: > On Sat, Apr 15 2023 at 09:22, Brian Gerst wrote: >> On Fri, Apr 14, 2023 at 7:45 PM Thomas Gleixner <tglx@linutronix.de> wrote: >>> @@ -248,10 +311,20 @@ SYM_INNER_LABEL(secondary_startup_64_no_ >>> * >>> * RDX contains the per-cpu offset >>> */ >>> - movq pcpu_hot + X86_current_task(%rdx), %rax >>> - movq TASK_threadsp(%rax), %rsp >>> + movq pcpu_hot + X86_top_of_stack(%rdx), %rsp >> >> Switching to using pcpu_hot.top_of_stack is ok, but it's not >> completely equivalent. top_of_stack points to the end of the pt_regs >> structure, while the kernel stack starts below pt_regs even for kernel >> threads. So you need to subtract PTREGS_SIZE from the stack pointer >> after this. >> >> This change should also be a separate patch. > > You're right on both counts. Actually no. We can't do that as this breaks suspend/resume (again). /me drops it.
--- a/arch/x86/include/asm/apic.h +++ b/arch/x86/include/asm/apic.h @@ -55,6 +55,8 @@ extern int local_apic_timer_c2_ok; extern int disable_apic; extern unsigned int lapic_timer_period; +extern int cpuid_to_apicid[]; + extern enum apic_intr_mode_id apic_intr_mode; enum apic_intr_mode_id { APIC_PIC, --- a/arch/x86/include/asm/realmode.h +++ b/arch/x86/include/asm/realmode.h @@ -52,6 +52,7 @@ struct trampoline_header { u64 efer; u32 cr4; u32 flags; + u32 lock; #endif }; @@ -64,6 +65,8 @@ extern unsigned long initial_stack; extern unsigned long initial_vc_handler; #endif +extern u32 *trampoline_lock; + extern unsigned char real_mode_blob[]; extern unsigned char real_mode_relocs[]; --- a/arch/x86/include/asm/smp.h +++ b/arch/x86/include/asm/smp.h @@ -198,4 +198,12 @@ extern unsigned int smpboot_control; #endif /* !__ASSEMBLY__ */ +/* Control bits for startup_64 */ +#define STARTUP_APICID_CPUID_1F 0x80000000 +#define STARTUP_APICID_CPUID_0B 0x40000000 +#define STARTUP_APICID_CPUID_01 0x20000000 + +/* Top 8 bits are reserved for control */ +#define STARTUP_PARALLEL_MASK 0xFF000000 + #endif /* _ASM_X86_SMP_H */ --- a/arch/x86/kernel/acpi/sleep.c +++ b/arch/x86/kernel/acpi/sleep.c @@ -16,6 +16,7 @@ #include <asm/cacheflush.h> #include <asm/realmode.h> #include <asm/hypervisor.h> +#include <asm/smp.h> #include <linux/ftrace.h> #include "../../realmode/rm/wakeup.h" @@ -127,7 +128,13 @@ int x86_acpi_suspend_lowlevel(void) * value is in the actual %rsp register. */ current->thread.sp = (unsigned long)temp_stack + sizeof(temp_stack); - smpboot_control = smp_processor_id(); + /* + * Ensure the CPU knows which one it is when it comes back, if + * it isn't in parallel mode and expected to work that out for + * itself. + */ + if (!(smpboot_control & STARTUP_PARALLEL_MASK)) + smpboot_control = smp_processor_id(); #endif initial_code = (unsigned long)wakeup_long64; saved_magic = 0x123456789abcdef0L; --- a/arch/x86/kernel/apic/apic.c +++ b/arch/x86/kernel/apic/apic.c @@ -2377,7 +2377,7 @@ static int nr_logical_cpuids = 1; /* * Used to store mapping between logical CPU IDs and APIC IDs. */ -static int cpuid_to_apicid[] = { +int cpuid_to_apicid[] = { [0 ... NR_CPUS - 1] = -1, }; --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -25,6 +25,7 @@ #include <asm/export.h> #include <asm/nospec-branch.h> #include <asm/fixmap.h> +#include <asm/smp.h> /* * We are not able to switch in one step to the final KERNEL ADDRESS SPACE @@ -234,8 +235,70 @@ SYM_INNER_LABEL(secondary_startup_64_no_ ANNOTATE_NOENDBR // above #ifdef CONFIG_SMP + /* + * For parallel boot, the APIC ID is retrieved from CPUID, and then + * used to look up the CPU number. For booting a single CPU, the + * CPU number is encoded in smpboot_control. + * + * Bit 31 STARTUP_APICID_CPUID_1F flag (use CPUID 0x1f) + * Bit 30 STARTUP_APICID_CPUID_0B flag (use CPUID 0x0b) + * Bit 29 STARTUP_APICID_CPUID_01 flag (use CPUID 0x01) + * Bit 0-23 CPU# if STARTUP_APICID_CPUID_xx flags are not set + */ movl smpboot_control(%rip), %ecx + testl $STARTUP_APICID_CPUID_1F, %ecx + jnz .Luse_cpuid_1f + testl $STARTUP_APICID_CPUID_0B, %ecx + jnz .Luse_cpuid_0b + testl $STARTUP_APICID_CPUID_01, %ecx + jnz .Luse_cpuid_01 + andl $(~STARTUP_PARALLEL_MASK), %ecx + jmp .Lsetup_cpu + +.Luse_cpuid_01: + mov $0x01, %eax + cpuid + mov %ebx, %edx + shr $24, %edx + jmp .Lsetup_AP + +.Luse_cpuid_0b: + mov $0x0B, %eax + xorl %ecx, %ecx + cpuid + jmp .Lsetup_AP + +.Luse_cpuid_1f: + mov $0x1f, %eax + xorl %ecx, %ecx + cpuid +.Lsetup_AP: + /* EDX contains the APIC ID of the current CPU */ + xorq %rcx, %rcx + leaq cpuid_to_apicid(%rip), %rbx + +.Lfind_cpunr: + cmpl (%rbx,%rcx,4), %edx + jz .Lsetup_cpu + inc %ecx +#ifdef CONFIG_FORCE_NR_CPUS + cmpl $NR_CPUS, %ecx +#else + cmpl nr_cpu_ids(%rip), %ecx +#endif + jb .Lfind_cpunr + + /* APIC ID not found in the table. Drop the trampoline lock and bail. */ + movq trampoline_lock(%rip), %rax + lock + btrl $0, (%rax) + +1: cli + hlt + jmp 1b + +.Lsetup_cpu: /* Get the per cpu offset for the given CPU# which is in ECX */ movq __per_cpu_offset(,%rcx,8), %rdx #else @@ -248,10 +311,20 @@ SYM_INNER_LABEL(secondary_startup_64_no_ * * RDX contains the per-cpu offset */ - movq pcpu_hot + X86_current_task(%rdx), %rax - movq TASK_threadsp(%rax), %rsp + movq pcpu_hot + X86_top_of_stack(%rdx), %rsp /* + * Now that this CPU is running on its own stack, drop the realmode + * protection. For the boot CPU the pointer is NULL! + */ + movq trampoline_lock(%rip), %rax + testq %rax, %rax + jz .Lsetup_gdt + lock + btrl $0, (%rax) + +.Lsetup_gdt: + /* * We must switch to a new descriptor in kernel space for the GDT * because soon the kernel won't have access anymore to the userspace * addresses where we're currently running on. We have to do that here @@ -435,6 +508,8 @@ SYM_DATA(initial_code, .quad x86_64_star #ifdef CONFIG_AMD_MEM_ENCRYPT SYM_DATA(initial_vc_handler, .quad handle_vc_boot_ghcb) #endif + +SYM_DATA(trampoline_lock, .quad 0); __FINITDATA __INIT --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -985,10 +985,7 @@ int common_cpu_up(unsigned int cpu, stru if (ret) return ret; -#ifdef CONFIG_X86_32 - /* Stack for startup_32 can be just as for start_secondary onwards */ per_cpu(pcpu_hot.top_of_stack, cpu) = task_top_of_stack(idle); -#endif return 0; } @@ -1014,7 +1011,7 @@ static int do_boot_cpu(int apicid, int c if (IS_ENABLED(CONFIG_X86_32)) { early_gdt_descr.address = (unsigned long)get_cpu_gdt_rw(cpu); initial_stack = idle->thread.sp; - } else { + } else if (!(smpboot_control & STARTUP_PARALLEL_MASK)) { smpboot_control = cpu; } --- a/arch/x86/realmode/init.c +++ b/arch/x86/realmode/init.c @@ -154,6 +154,9 @@ static void __init setup_real_mode(void) trampoline_header->flags = 0; + trampoline_lock = &trampoline_header->lock; + *trampoline_lock = 0; + trampoline_pgd = (u64 *) __va(real_mode_header->trampoline_pgd); /* Map the real mode stub as virtual == physical */ --- a/arch/x86/realmode/rm/trampoline_64.S +++ b/arch/x86/realmode/rm/trampoline_64.S @@ -37,6 +37,24 @@ .text .code16 +.macro LOAD_REALMODE_ESP + /* + * Make sure only one CPU fiddles with the realmode stack + */ +.Llock_rm\@: + btl $0, tr_lock + jnc 2f + pause + jmp .Llock_rm\@ +2: + lock + btsl $0, tr_lock + jc .Llock_rm\@ + + # Setup stack + movl $rm_stack_end, %esp +.endm + .balign PAGE_SIZE SYM_CODE_START(trampoline_start) cli # We should be safe anyway @@ -49,8 +67,7 @@ SYM_CODE_START(trampoline_start) mov %ax, %es mov %ax, %ss - # Setup stack - movl $rm_stack_end, %esp + LOAD_REALMODE_ESP call verify_cpu # Verify the cpu supports long mode testl %eax, %eax # Check for return code @@ -93,8 +110,7 @@ SYM_CODE_START(sev_es_trampoline_start) mov %ax, %es mov %ax, %ss - # Setup stack - movl $rm_stack_end, %esp + LOAD_REALMODE_ESP jmp .Lswitch_to_protected SYM_CODE_END(sev_es_trampoline_start) @@ -177,7 +193,7 @@ SYM_CODE_START(pa_trampoline_compat) * In compatibility mode. Prep ESP and DX for startup_32, then disable * paging and complete the switch to legacy 32-bit mode. */ - movl $rm_stack_end, %esp + LOAD_REALMODE_ESP movw $__KERNEL_DS, %dx movl $(CR0_STATE & ~X86_CR0_PG), %eax @@ -241,6 +257,7 @@ SYM_DATA_START(trampoline_header) SYM_DATA(tr_efer, .space 8) SYM_DATA(tr_cr4, .space 4) SYM_DATA(tr_flags, .space 4) + SYM_DATA(tr_lock, .space 4) SYM_DATA_END(trampoline_header) #include "trampoline_common.S"