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Piccoli" Subject: [PATCH v13 06/11] x86/smpboot: Remove initial_stack on 64-bit Date: Thu, 2 Mar 2023 11:12:22 +0000 Message-Id: <20230302111227.2102545-7-usama.arif@bytedance.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230302111227.2102545-1-usama.arif@bytedance.com> References: <20230302111227.2102545-1-usama.arif@bytedance.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Brian Gerst In order to facilitate parallel startup, start to eliminate some of the global variables passing information to CPUs in the startup path. However, start by introducing one more: smpboot_control. For now this merely holds the CPU# of the CPU which is coming up. Each CPU can then find its own per-cpu data, and everything else it needs can be found from there, allowing the other global variables to be removed. First to be removed is initial_stack. Each CPU can load %rsp from its current_task->thread.sp instead. That is already set up with the correct idle thread for APs. Set up the .sp field in INIT_THREAD on x86 so that the BSP also finds a suitable stack pointer in the static per-cpu data when coming up on first boot. On resume from S3, the CPU needs a temporary stack because its idle task is already active. Instead of setting initial_stack, the sleep code can simply set its own current->thread.sp to point to the temporary stack. Nobody else cares about ->thread.sp for a thread which is currently on a CPU, because the true value is actually in the %rsp register. Which is restored with the rest of the CPU context in do_suspend_lowlevel(). Signed-off-by: Brian Gerst Reviewed-by: David Woodhouse Signed-off-by: David Woodhouse Tested-by: Usama Arif Signed-off-by: Usama Arif Tested-by: Guilherme G. Piccoli --- arch/x86/include/asm/processor.h | 6 ++++- arch/x86/include/asm/smp.h | 5 +++- arch/x86/kernel/acpi/sleep.c | 20 +++++++++++++-- arch/x86/kernel/asm-offsets.c | 1 + arch/x86/kernel/head_64.S | 43 +++++++++++++++++++++----------- arch/x86/kernel/smpboot.c | 7 +++++- arch/x86/xen/xen-head.S | 2 +- 7 files changed, 63 insertions(+), 21 deletions(-) diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 4e35c66edeb7..bdde7316e75b 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -648,7 +648,11 @@ static inline void spin_lock_prefetch(const void *x) #define KSTK_ESP(task) (task_pt_regs(task)->sp) #else -#define INIT_THREAD { } +extern unsigned long __end_init_task[]; + +#define INIT_THREAD { \ + .sp = (unsigned long)&__end_init_task - sizeof(struct pt_regs), \ +} extern unsigned long KSTK_ESP(struct task_struct *task); diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h index b4dbb20dab1a..bf2c51df9e0b 100644 --- a/arch/x86/include/asm/smp.h +++ b/arch/x86/include/asm/smp.h @@ -199,5 +199,8 @@ extern void nmi_selftest(void); #define nmi_selftest() do { } while (0) #endif -#endif /* __ASSEMBLY__ */ +extern unsigned int smpboot_control; + +#endif /* !__ASSEMBLY__ */ + #endif /* _ASM_X86_SMP_H */ diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c index 3b7f4cdbf2e0..1b4c43d0819a 100644 --- a/arch/x86/kernel/acpi/sleep.c +++ b/arch/x86/kernel/acpi/sleep.c @@ -111,13 +111,29 @@ int x86_acpi_suspend_lowlevel(void) saved_magic = 0x12345678; #else /* CONFIG_64BIT */ #ifdef CONFIG_SMP - initial_stack = (unsigned long)temp_stack + sizeof(temp_stack); + /* + * As each CPU starts up, it will find its own stack pointer + * from its current_task->thread.sp. Typically that will be + * the idle thread for a newly-started AP, or even the boot + * CPU which will find it set to &init_task in the static + * per-cpu data. + * + * Make the resuming CPU use the temporary stack at startup + * by setting current->thread.sp to point to that. The true + * %rsp will be restored with the rest of the CPU context, + * by do_suspend_lowlevel(). And unwinders don't care about + * the abuse of ->thread.sp because it's a dead variable + * while the thread is running on the CPU anyway; the true + * value is in the actual %rsp register. + */ + current->thread.sp = (unsigned long)temp_stack + sizeof(temp_stack); early_gdt_descr.address = (unsigned long)get_cpu_gdt_rw(smp_processor_id()); initial_gs = per_cpu_offset(smp_processor_id()); + smpboot_control = smp_processor_id(); #endif initial_code = (unsigned long)wakeup_long64; - saved_magic = 0x123456789abcdef0L; + saved_magic = 0x123456789abcdef0L; #endif /* CONFIG_64BIT */ /* diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c index 82c783da16a8..797ae1a15c91 100644 --- a/arch/x86/kernel/asm-offsets.c +++ b/arch/x86/kernel/asm-offsets.c @@ -108,6 +108,7 @@ static void __used common(void) OFFSET(TSS_sp1, tss_struct, x86_tss.sp1); OFFSET(TSS_sp2, tss_struct, x86_tss.sp2); OFFSET(X86_top_of_stack, pcpu_hot, top_of_stack); + OFFSET(X86_current_task, pcpu_hot, current_task); #ifdef CONFIG_CALL_DEPTH_TRACKING OFFSET(X86_call_depth, pcpu_hot, call_depth); #endif diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 222efd4a09bc..cc1b145055ac 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -61,8 +61,8 @@ SYM_CODE_START_NOALIGN(startup_64) * tables and then reload them. */ - /* Set up the stack for verify_cpu(), similar to initial_stack below */ - leaq (__end_init_task - FRAME_SIZE)(%rip), %rsp + /* Set up the stack for verify_cpu() */ + leaq (__end_init_task - PTREGS_SIZE)(%rip), %rsp leaq _text(%rip), %rdi @@ -241,6 +241,24 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) UNWIND_HINT_EMPTY ANNOTATE_NOENDBR // above +#ifdef CONFIG_SMP + movl smpboot_control(%rip), %ecx + + /* Get the per cpu offset for the given CPU# which is in ECX */ + movq __per_cpu_offset(,%rcx,8), %rdx +#else + xorl %edx, %edx /* zero-extended to clear all of RDX */ +#endif /* CONFIG_SMP */ + + /* + * Setup a boot time stack - Any secondary CPU will have lost its stack + * by now because the cr3-switch above unmaps the real-mode stack. + * + * RDX contains the per-cpu offset + */ + movq pcpu_hot + X86_current_task(%rdx), %rax + movq TASK_threadsp(%rax), %rsp + /* * 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 @@ -275,12 +293,6 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) movl initial_gs+4(%rip),%edx wrmsr - /* - * Setup a boot time stack - Any secondary CPU will have lost its stack - * by now because the cr3-switch above unmaps the real-mode stack - */ - movq initial_stack(%rip), %rsp - /* Setup and Load IDT */ pushq %rsi call early_setup_idt @@ -372,7 +384,11 @@ SYM_CODE_END(secondary_startup_64) SYM_CODE_START(start_cpu0) ANNOTATE_NOENDBR UNWIND_HINT_EMPTY - movq initial_stack(%rip), %rsp + + /* Find the idle task stack */ + movq PER_CPU_VAR(pcpu_hot) + X86_current_task, %rcx + movq TASK_threadsp(%rcx), %rsp + jmp .Ljump_to_C_code SYM_CODE_END(start_cpu0) #endif @@ -420,12 +436,6 @@ SYM_DATA(initial_gs, .quad INIT_PER_CPU_VAR(fixed_percpu_data)) #ifdef CONFIG_AMD_MEM_ENCRYPT SYM_DATA(initial_vc_handler, .quad handle_vc_boot_ghcb) #endif - -/* - * The FRAME_SIZE gap is a convention which helps the in-kernel unwinder - * reliably detect the end of the stack. - */ -SYM_DATA(initial_stack, .quad init_thread_union + THREAD_SIZE - FRAME_SIZE) __FINITDATA __INIT @@ -660,6 +670,9 @@ SYM_DATA_END(level1_fixmap_pgt) SYM_DATA(early_gdt_descr, .word GDT_ENTRIES*8-1) SYM_DATA_LOCAL(early_gdt_descr_base, .quad INIT_PER_CPU_VAR(gdt_page)) + .align 16 +SYM_DATA(smpboot_control, .long 0) + .align 16 /* This must match the first entry in level2_kernel_pgt */ SYM_DATA(phys_base, .quad 0x0) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index b18c1385e181..62e3bf37f0b8 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1112,7 +1112,12 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle, idle->thread.sp = (unsigned long)task_pt_regs(idle); early_gdt_descr.address = (unsigned long)get_cpu_gdt_rw(cpu); initial_code = (unsigned long)start_secondary; - initial_stack = idle->thread.sp; + + if (IS_ENABLED(CONFIG_X86_32)) { + initial_stack = idle->thread.sp; + } else { + smpboot_control = cpu; + } /* Enable the espfix hack for this CPU */ init_espfix_ap(cpu); diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S index ffaa62167f6e..6bd391476656 100644 --- a/arch/x86/xen/xen-head.S +++ b/arch/x86/xen/xen-head.S @@ -49,7 +49,7 @@ SYM_CODE_START(startup_xen) ANNOTATE_NOENDBR cld - mov initial_stack(%rip), %rsp + leaq (__end_init_task - PTREGS_SIZE)(%rip), %rsp /* Set up %gs. * -- 2.25.1