[PATCH hyperv-next] arch/x86: Provide the CPU number in the wakeup AP callback

Roman Kisel
2025-04-28T22:59:51Z

When starting APs, confidential guests and paravisor guests
need to know the CPU number, and the pattern of using the linear
search has emerged in several places. With N processors that leads
to the O(N^2) time complexity.

Provide the CPU number in the AP wake up callback so that one can
get the CPU number in constant time.

Suggested-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
---
arch/x86/coco/sev/core.c | 18 ++++++++----------
arch/x86/hyperv/hv_vtl.c | 17 +++++++----------
arch/x86/hyperv/ivm.c | 8 +++++++-
arch/x86/include/asm/apic.h | 14 ++++++++++----
arch/x86/include/asm/mshyperv.h | 5 +++--
arch/x86/kernel/acpi/madt_wakeup.c | 8 +++++++-
arch/x86/kernel/apic/apic_noop.c | 2 +-
arch/x86/kernel/apic/x2apic_uv_x.c | 7 ++++++-
arch/x86/kernel/smpboot.c | 19 +++++++++++++++----
9 files changed, 64 insertions(+), 34 deletions(-)

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 82492efc5d94..063f176854fd 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -1179,17 +1179,24 @@ static void snp_cleanup_vmsa(struct sev_es_save_area *vmsa, int apic_id)
free_page((unsigned long)vmsa);
}

-static int wakeup_cpu_via_vmgexit(u32 apic_id, unsigned long start_ip)
+static int wakeup_cpu_via_vmgexit(struct wakeup_secondary_cpu_data *wakeup)
{
struct sev_es_save_area *cur_vmsa, *vmsa;
struct ghcb_state state;
+ unsigned long start_ip;
struct svsm_ca *caa;
unsigned long flags;
struct ghcb *ghcb;
u8 sipi_vector;
int cpu, ret;
+ u32 apic_id;
u64 cr4;

+
+ cpu = wakeup->cpu;
+ apic_id = wakeup->apicid;
+ start_ip = wakeup->start_ip;
+
/*
* The hypervisor SNP feature support check has happened earlier, just check
* the AP_CREATION one here.
@@ -1208,15 +1215,6 @@ static int wakeup_cpu_via_vmgexit(u32 apic_id, unsigned long start_ip)

/* Override start_ip with known protected guest start IP */
start_ip = real_mode_header->sev_es_trampoline_start;
-
- /* Find the logical CPU for the APIC ID */
- for_each_present_cpu(cpu) {
- if (arch_match_cpu_phys_id(cpu, apic_id))
- break;
- }
- if (cpu >= nr_cpu_ids)
- return -EINVAL;
-
cur_vmsa = per_cpu(sev_vmsa, cpu);

/*
diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
index 582fe820e29c..7ed3c639d612 100644
--- a/arch/x86/hyperv/hv_vtl.c
+++ b/arch/x86/hyperv/hv_vtl.c
@@ -237,17 +237,14 @@ static int hv_vtl_apicid_to_vp_id(u32 apic_id)
return ret;
}

-static int hv_vtl_wakeup_secondary_cpu(u32 apicid, unsigned long start_eip)
+static int hv_vtl_wakeup_secondary_cpu(struct wakeup_secondary_cpu_data *wakeup)
{
- int vp_id, cpu;
+ unsigned long start_ip;
+ u32 apicid;
+ int vp_id;

- /* Find the logical CPU for the APIC ID */
- for_each_present_cpu(cpu) {
- if (arch_match_cpu_phys_id(cpu, apicid))
- break;
- }
- if (cpu >= nr_cpu_ids)
- return -EINVAL;
+ apicid = wakeup->apicid;
+ start_ip = wakeup->start_ip;

pr_debug("Bringing up CPU with APIC ID %d in VTL2...\n", apicid);
vp_id = hv_vtl_apicid_to_vp_id(apicid);
@@ -261,7 +258,7 @@ static int hv_vtl_wakeup_secondary_cpu(u32 apicid, unsigned long start_eip)
return -EINVAL;
}

- return hv_vtl_bringup_vcpu(vp_id, cpu, start_eip);
+ return hv_vtl_bringup_vcpu(vp_id, wakeup->cpu, start_ip);
}

int __init hv_vtl_early_init(void)
diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index c0039a90e9e0..6037cabc1ae0 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -9,6 +9,7 @@
#include <linux/bitfield.h>
#include <linux/types.h>
#include <linux/slab.h>
+#include <asm/apic.h>
#include <asm/svm.h>
#include <asm/sev.h>
#include <asm/io.h>
@@ -288,7 +289,7 @@ static void snp_cleanup_vmsa(struct sev_es_save_area *vmsa)
free_page((unsigned long)vmsa);
}

-int hv_snp_boot_ap(u32 cpu, unsigned long start_ip)
+int hv_snp_boot_ap(struct wakeup_secondary_cpu_data *wakeup)
{
struct sev_es_save_area *vmsa = (struct sev_es_save_area *)
__get_free_page(GFP_KERNEL | __GFP_ZERO);
@@ -296,11 +297,16 @@ int hv_snp_boot_ap(u32 cpu, unsigned long start_ip)
struct desc_ptr gdtr;
u64 ret, retry = 5;
struct hv_enable_vp_vtl *start_vp_input;
+ unsigned long start_ip;
unsigned long flags;
+ u32 cpu;

if (!vmsa)
return -ENOMEM;

+ cpu = wakeup->cpu;
+ start_ip = wakeup->apicid;
+
native_store_gdt(&gdtr);

vmsa->gdtr.base = gdtr.address;
diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index f21ff1932699..7e660125f749 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -262,6 +262,12 @@ extern void __init check_x2apic(void);

struct irq_data;

+struct wakeup_secondary_cpu_data {
+ int cpu;
+ u32 apicid;
+ unsigned long start_ip;
+};
+
/*
* Copyright 2004 James Cleverdon, IBM.
*
@@ -313,9 +319,9 @@ struct apic {
u32 (*get_apic_id)(u32 id);

/* wakeup_secondary_cpu */
- int (*wakeup_secondary_cpu)(u32 apicid, unsigned long start_eip);
+ int (*wakeup_secondary_cpu)(struct wakeup_secondary_cpu_data *data);
/* wakeup secondary CPU using 64-bit wakeup point */
- int (*wakeup_secondary_cpu_64)(u32 apicid, unsigned long start_eip);
+ int (*wakeup_secondary_cpu_64)(struct wakeup_secondary_cpu_data *data);

char *name;
};
@@ -333,8 +339,8 @@ struct apic_override {
void (*send_IPI_self)(int vector);
u64 (*icr_read)(void);
void (*icr_write)(u32 low, u32 high);
- int (*wakeup_secondary_cpu)(u32 apicid, unsigned long start_eip);
- int (*wakeup_secondary_cpu_64)(u32 apicid, unsigned long start_eip);
+ int (*wakeup_secondary_cpu)(struct wakeup_secondary_cpu_data *data);
+ int (*wakeup_secondary_cpu_64)(struct wakeup_secondary_cpu_data *data);
};

/*
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 07aadf0e839f..62c64778ad01 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -6,6 +6,7 @@
#include <linux/nmi.h>
#include <linux/msi.h>
#include <linux/io.h>
+#include <asm/apic.h>
#include <asm/nospec-branch.h>
#include <asm/paravirt.h>
#include <hyperv/hvhdk.h>
@@ -268,11 +269,11 @@ int hv_unmap_ioapic_interrupt(int ioapic_id, struct hv_interrupt_entry *entry);
#ifdef CONFIG_AMD_MEM_ENCRYPT
bool hv_ghcb_negotiate_protocol(void);
void __noreturn hv_ghcb_terminate(unsigned int set, unsigned int reason);
-int hv_snp_boot_ap(u32 cpu, unsigned long start_ip);
+int hv_snp_boot_ap(struct wakeup_secondary_cpu_data *wakeup);
#else
static inline bool hv_ghcb_negotiate_protocol(void) { return false; }
static inline void hv_ghcb_terminate(unsigned int set, unsigned int reason) {}
-static inline int hv_snp_boot_ap(u32 cpu, unsigned long start_ip) { return 0; }
+static inline int hv_snp_boot_ap(struct wakeup_secondary_cpu_data *wakeup) { return 0; }
#endif

#if defined(CONFIG_AMD_MEM_ENCRYPT) || defined(CONFIG_INTEL_TDX_GUEST)
diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index d5ef6215583b..5de1bd4e49ed 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -169,8 +169,14 @@ static int __init acpi_mp_setup_reset(u64 reset_vector)
return 0;
}

-static int acpi_wakeup_cpu(u32 apicid, unsigned long start_ip)
+static int acpi_wakeup_cpu(struct wakeup_secondary_cpu_data *wakeup)
{
+ unsigned long start_ip;
+ u32 apicid;
+
+ start_ip = wakeup->start_ip;
+ apicid = wakeup->apicid;
+
if (!acpi_mp_wake_mailbox_paddr) {
pr_warn_once("No MADT mailbox: cannot bringup secondary CPUs. Booting with kexec?\n");
return -EOPNOTSUPP;
diff --git a/arch/x86/kernel/apic/apic_noop.c b/arch/x86/kernel/apic/apic_noop.c
index b5bb7a2e8340..dd4ba29042f9 100644
--- a/arch/x86/kernel/apic/apic_noop.c
+++ b/arch/x86/kernel/apic/apic_noop.c
@@ -27,7 +27,7 @@ static void noop_send_IPI_allbutself(int vector) { }
static void noop_send_IPI_all(int vector) { }
static void noop_send_IPI_self(int vector) { }
static void noop_apic_icr_write(u32 low, u32 id) { }
-static int noop_wakeup_secondary_cpu(u32 apicid, unsigned long start_eip) { return -1; }
+static int noop_wakeup_secondary_cpu(struct wakeup_secondary_cpu_data *data) { return -1; }
static u64 noop_apic_icr_read(void) { return 0; }
static u32 noop_get_apic_id(u32 apicid) { return 0; }
static void noop_apic_eoi(void) { }
diff --git a/arch/x86/kernel/apic/x2apic_uv_x.c b/arch/x86/kernel/apic/x2apic_uv_x.c
index 7fef504ca508..b76f865c31ef 100644
--- a/arch/x86/kernel/apic/x2apic_uv_x.c
+++ b/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -667,11 +667,16 @@ static __init void build_uv_gr_table(void)
}
}

-static int uv_wakeup_secondary(u32 phys_apicid, unsigned long start_rip)
+static int uv_wakeup_secondary(struct wakeup_secondary_cpu_data *wakeup)
{
+ unsigned long start_rip;
unsigned long val;
+ u32 phys_apicid;
int pnode;

+ phys_apicid = wakeup->apicid;
+ start_rip = wakeup->start_ip;
+
pnode = uv_apicid_to_pnode(phys_apicid);

val = (1UL << UVH_IPI_INT_SEND_SHFT) |
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index c10850ae6f09..341620f1e1fe 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -715,8 +715,14 @@ static void send_init_sequence(u32 phys_apicid)
/*
* Wake up AP by INIT, INIT, STARTUP sequence.
*/
-static int wakeup_secondary_cpu_via_init(u32 phys_apicid, unsigned long start_eip)
+static int wakeup_secondary_cpu_via_init(struct wakeup_secondary_cpu_data *wakeup)
{
+ unsigned long start_eip;
+ u32 phys_apicid;
+
+ start_eip = wakeup->start_ip;
+ phys_apicid = wakeup->apicid;
+
unsigned long send_status = 0, accept_status = 0;
int num_starts, j, maxlvt;

@@ -865,6 +871,7 @@ int common_cpu_up(unsigned int cpu, struct task_struct *idle)
static int do_boot_cpu(u32 apicid, int cpu, struct task_struct *idle)
{
unsigned long start_ip = real_mode_header->trampoline_start;
+ struct wakeup_secondary_cpu_data wakeup;
int ret;

#ifdef CONFIG_X86_64
@@ -906,6 +913,10 @@ static int do_boot_cpu(u32 apicid, int cpu, struct task_struct *idle)
}
}

+ wakeup.cpu = cpu;
+ wakeup.apicid = apicid;
+ wakeup.start_ip = start_ip;
+
smp_mb();

/*
@@ -916,11 +927,11 @@ static int do_boot_cpu(u32 apicid, int cpu, struct task_struct *idle)
* - Use an INIT boot APIC message
*/
if (apic->wakeup_secondary_cpu_64)
- ret = apic->wakeup_secondary_cpu_64(apicid, start_ip);
+ ret = apic->wakeup_secondary_cpu_64(&wakeup);
else if (apic->wakeup_secondary_cpu)
- ret = apic->wakeup_secondary_cpu(apicid, start_ip);
+ ret = apic->wakeup_secondary_cpu(&wakeup);
else
- ret = wakeup_secondary_cpu_via_init(apicid, start_ip);
+ ret = wakeup_secondary_cpu_via_init(&wakeup);

/* If the wakeup mechanism failed, cleanup the warm reset vector */
if (ret)

base-commit: 628cc040b3a2980df6032766e8ef0688e981ab95
--
2.43.0