x86/smpboot: Support parallel startup of secondary CPUs

To allow for parallel AP bringup, we need to avoid the use of global
variables for passing information to the APs, as well as preventing them
from all trying to use the same real-mode stack simultaneously.

So, introduce a 'lock' field in struct trampoline_header to use as a
simple bit-spinlock for the real-mode stack. That lock also protects
the global variables initial_gs, initial_stack and early_gdt_descr,
which can now be calculated...

So how do we calculate those addresses? Well, they they can all be found
from the per_cpu data for this CPU. Simples! Except... how does it know
what its CPU# is? OK, we export the cpuid_to_apicid[] array and it can
search it to find its APIC ID in there.

But now you whine at me that it doesn't even know its APIC ID? Well, if
it's a relatively modern CPU then the APIC ID is in CPUID leaf 0x0B so
we can use that. Otherwise... erm... OK, otherwise it can't have parallel
CPU bringup for now. We'll still use a global variable for those CPUs and
bring them up one at a time.

So add a global 'smpboot_control' field which either contains the APIC
ID, or a flag indicating that it can be found in CPUID.

This adds the 'do_parallel_bringup' flag in preparation but doesn't
actually enable parallel bringup yet.

[ dwmw2: Minor tweaks, write a commit message ]
Not-signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
index 5db5d083c87322ec4913252d1c22752b85d517f4..e1cc4bc746bc872faaaa972fc2d35dca068fcd0f 100644 (file)
--- a/arch/x86/include/asm/realmode.h
+++ b/arch/x86/include/asm/realmode.h
@@ -51,6 +51,7 @@ 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[];
 

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 81a0211a372d3d268671ecfa1d554816481006bc..ea6440fe5b61275c7f52da2535dfb43657f16b10 100644 (file)
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -196,5 +196,11 @@ extern void nmi_selftest(void);
 #define nmi_selftest() do { } while (0)
 #endif
 
-#endif /* __ASSEMBLY__ */
+extern unsigned int smpboot_control;
+
+#endif /* !__ASSEMBLY__ */
+
+/* Control bits for startup_64 */
+#define        STARTUP_PARALLEL        0x80000000
+
 #endif /* _ASM_X86_SMP_H */

diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
index 3f85fcae450ce2fb89b8c466d6872815491f493f..9598ebf4f9d640ebcb84ab9f89b36fd196a6134d 100644 (file)
--- a/arch/x86/kernel/acpi/sleep.c
+++ b/arch/x86/kernel/acpi/sleep.c
@@ -114,6 +114,7 @@ int x86_acpi_suspend_lowlevel(void)
        early_gdt_descr.address =
                        (unsigned long)get_cpu_gdt_rw(smp_processor_id());
        initial_gs = per_cpu_offset(smp_processor_id());
+       smpboot_control = 0;
 #endif
        initial_code = (unsigned long)wakeup_long64;
        saved_magic = 0x123456789abcdef0L;

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index b70344bf660083bbeb998bc0b74737a21047d46b..5b20e051d84c354bba20261019215a38f20e0f5c 100644 (file)
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2335,7 +2335,7 @@ 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,
 };
 

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index d8b3ebd2bb85fe1ff903455de990074eb96e78e9..3e4c3c416bce38335cc026af6eebb2a9e111fdb2 100644 (file)
--- 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
@@ -176,6 +177,62 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
 1:
        UNWIND_HINT_EMPTY
 
+       /*
+        * Is this the boot CPU coming up? If so everything is available
+        * in initial_gs, initial_stack and early_gdt_descr.
+        */
+       movl    smpboot_control(%rip), %eax
+       testl   %eax, %eax
+       jz      .Lsetup_cpu
+
+       /*
+        * Secondary CPUs find out the offsets via the APIC ID. For parallel
+        * boot the APIC ID is retrieved from CPUID, otherwise it's encoded
+        * in smpboot_control:
+        * Bit 0-30     APIC ID if STARTUP_PARALLEL is not set
+        * Bit 31       Parallel boot flag (use CPUID leaf 0x0b for APIC ID).
+        */
+       testl   $STARTUP_PARALLEL, %eax
+       jz      .Lsetup_AP
+
+       mov     $0x0B, %eax
+       xorl    %ecx, %ecx
+       cpuid
+       mov     %edx, %eax
+
+.Lsetup_AP:
+       /* EAX contains the APICID of the current CPU */
+       xorl    %ecx, %ecx
+       leaq    cpuid_to_apicid(%rip), %rbx
+
+.Lfind_cpunr:
+       cmpl    (%rbx), %eax
+       jz      .Linit_cpu_data
+       addq    $4, %rbx
+       addq    $8, %rcx
+       jmp     .Lfind_cpunr
+
+.Linit_cpu_data:
+       /* Get the per cpu offset */
+       leaq    __per_cpu_offset(%rip), %rbx
+       addq    %rcx, %rbx
+       movq    (%rbx), %rbx
+       /* Save it for GS BASE setup */
+       movq    %rbx, initial_gs(%rip)
+
+       /* Calculate the GDT address */
+       movq    $gdt_page, %rcx
+       addq    %rbx, %rcx
+       movq    %rcx, early_gdt_descr_base(%rip)
+
+       /* Find the idle task stack */
+       movq    $idle_threads, %rcx
+       addq    %rbx, %rcx
+       movq    (%rcx), %rcx
+       movq    TASK_threadsp(%rcx), %rcx
+       movq    %rcx, initial_stack(%rip)
+
+.Lsetup_cpu:
        /*
         * 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
@@ -216,6 +273,14 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
         */
        movq initial_stack(%rip), %rsp
 
+       /* Drop the realmode protection. For the boot CPU the pointer is NULL! */
+       movq    trampoline_lock(%rip), %rax
+       testq   %rax, %rax
+       jz      .Lsetup_idt
+       lock
+       btrl    $0, (%rax)
+
+.Lsetup_idt:
        /* Setup and Load IDT */
        pushq   %rsi
        call    early_setup_idt
@@ -347,6 +412,7 @@ SYM_DATA(initial_vc_handler,        .quad handle_vc_boot_ghcb)
  * reliably detect the end of the stack.
  */
 SYM_DATA(initial_stack, .quad init_thread_union + THREAD_SIZE - FRAME_SIZE)
+SYM_DATA(trampoline_lock, .quad 0);
        __FINITDATA
 
        __INIT
@@ -572,6 +638,9 @@ 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 7a763b84b6e53ab2dbe54cf685bfbef6211b179f..f7030a27a1786c84d470ea4d3b45a8d979d21a3f 100644 (file)
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -797,6 +797,16 @@ static int __init cpu_init_udelay(char *str)
 }
 early_param("cpu_init_udelay", cpu_init_udelay);
 
+static bool do_parallel_bringup = true;
+
+static int __init no_parallel_bringup(char *str)
+{
+       do_parallel_bringup = false;
+
+       return 0;
+}
+early_param("no_parallel_bringup", no_parallel_bringup);
+
 static void __init smp_quirk_init_udelay(void)
 {
        /* if cmdline changed it from default, leave it alone */
@@ -1104,9 +1114,16 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,
        unsigned long boot_error = 0;
 
        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)) {
+               early_gdt_descr.address = (unsigned long)get_cpu_gdt_rw(cpu);
+               initial_stack  = idle->thread.sp;
+       } else if (do_parallel_bringup) {
+               smpboot_control = STARTUP_PARALLEL;
+       } else {
+               smpboot_control = apicid;
+       }
 
        /* Enable the espfix hack for this CPU */
        init_espfix_ap(cpu);
@@ -1505,6 +1522,15 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
        smp_quirk_init_udelay();
 
        speculative_store_bypass_ht_init();
+
+       /*
+        * We can do 64-bit AP bringup in parallel if the CPU reports its
+        * APIC ID in CPUID leaf 0x0B. Otherwise it's too hard. And not
+        * for SEV-ES guests because they can't use CPUID that early.
+        */
+       if (IS_ENABLED(CONFIG_X86_32) || boot_cpu_data.cpuid_level < 0x0B ||
+           cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
+               do_parallel_bringup = false;
 }
 
 void arch_thaw_secondary_cpus_begin(void)

diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index 4a3da7592b99c938eed72dd583475bef4ae131a1..7dc2e817bd02f6084791140341b14476a329366b 100644 (file)
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -127,6 +127,9 @@ 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);
        trampoline_pgd[0] = trampoline_pgd_entry.pgd;
        trampoline_pgd[511] = init_top_pgt[511].pgd;

diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
index cc8391f86cdb61469b2b775a64490e470b2ef534..12a540904e803a695d1b096c8242732bc6e3a1c3 100644 (file)
--- a/arch/x86/realmode/rm/trampoline_64.S
+++ b/arch/x86/realmode/rm/trampoline_64.S
@@ -49,6 +49,19 @@ SYM_CODE_START(trampoline_start)
        mov     %ax, %es
        mov     %ax, %ss
 
+       /*
+        * 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
 
@@ -192,6 +205,7 @@ 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"

diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index f6bc0bc8a2aab322c0f6e89f1d53a4302878e438..934e64ff4eed3ce50d42eb1eb0b0da2f9f7c43c0 100644 (file)
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -25,7 +25,7 @@
  * For the hotplug case we keep the task structs around and reuse
  * them.
  */
-static DEFINE_PER_CPU(struct task_struct *, idle_threads);
+DEFINE_PER_CPU(struct task_struct *, idle_threads);
 
 struct task_struct *idle_thread_get(unsigned int cpu)
 {