x86/hyperv: Fix APIC ID and VP index confusion in hv_snp_boot_ap()

To start an application processor in SNP-isolated guest, a hypercall
is used that takes a virtual processor index. The hv_snp_boot_ap()
function uses that START_VP hypercall but passes as VP index to it
what it receives as a wakeup_secondary_cpu_64 callback: the APIC ID.

As those two aren't generally interchangeable, that may lead to hung
APs if the VP index and the APIC ID don't match up.

Update the parameter names to avoid confusion as to what the parameter
is. Use the APIC ID to the VP index conversion to provide the correct
input to the hypercall.

Cc: stable@vger.kernel.org
Fixes: 44676bb9d566 ("x86/hyperv: Add smp support for SEV-SNP guest")
Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20250507182227.7421-2-romank@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20250507182227.7421-2-romank@linux.microsoft.com>

3 files changed, 59 insertions, 40 deletions

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 3b569291dfed..9a8fc144e195 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -672,3 +672,36 @@ bool hv_is_hyperv_initialized(void)
 	return hypercall_msr.enable;
 }
 EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);
+
+int hv_apicid_to_vp_index(u32 apic_id)
+{
+	u64 control;
+	u64 status;
+	unsigned long irq_flags;
+	struct hv_get_vp_from_apic_id_in *input;
+	u32 *output, ret;
+
+	local_irq_save(irq_flags);
+
+	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
+	memset(input, 0, sizeof(*input));
+	input->partition_id = HV_PARTITION_ID_SELF;
+	input->apic_ids[0] = apic_id;
+
+	output = *this_cpu_ptr(hyperv_pcpu_output_arg);
+
+	control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_INDEX_FROM_APIC_ID;
+	status = hv_do_hypercall(control, input, output);
+	ret = output[0];
+
+	local_irq_restore(irq_flags);
+
+	if (!hv_result_success(status)) {
+		pr_err("failed to get vp index from apic id %d, status %#llx\n",
+		       apic_id, status);
+		return -EINVAL;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(hv_apicid_to_vp_index);
diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
index ac3d27a766d5..2f32ac1ae40e 100644
--- a/arch/x86/hyperv/hv_vtl.c
+++ b/arch/x86/hyperv/hv_vtl.c
@@ -211,41 +211,9 @@ free_lock:
 	return ret;
 }
 
-static int hv_vtl_apicid_to_vp_id(u32 apic_id)
-{
-	u64 control;
-	u64 status;
-	unsigned long irq_flags;
-	struct hv_get_vp_from_apic_id_in *input;
-	u32 *output, ret;
-
-	local_irq_save(irq_flags);
-
-	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
-	memset(input, 0, sizeof(*input));
-	input->partition_id = HV_PARTITION_ID_SELF;
-	input->apic_ids[0] = apic_id;
-
-	output = *this_cpu_ptr(hyperv_pcpu_output_arg);
-
-	control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_ID_FROM_APIC_ID;
-	status = hv_do_hypercall(control, input, output);
-	ret = output[0];
-
-	local_irq_restore(irq_flags);
-
-	if (!hv_result_success(status)) {
-		pr_err("failed to get vp id from apic id %d, status %#llx\n",
-		       apic_id, status);
-		return -EINVAL;
-	}
-
-	return ret;
-}
-
 static int hv_vtl_wakeup_secondary_cpu(u32 apicid, unsigned long start_eip)
 {
-	int vp_id, cpu;
+	int vp_index, cpu;
 
 	/* Find the logical CPU for the APIC ID */
 	for_each_present_cpu(cpu) {
@@ -256,18 +224,18 @@ static int hv_vtl_wakeup_secondary_cpu(u32 apicid, unsigned long start_eip)
 		return -EINVAL;
 
 	pr_debug("Bringing up CPU with APIC ID %d in VTL2...\n", apicid);
-	vp_id = hv_vtl_apicid_to_vp_id(apicid);
+	vp_index = hv_apicid_to_vp_index(apicid);
 
-	if (vp_id < 0) {
+	if (vp_index < 0) {
 		pr_err("Couldn't find CPU with APIC ID %d\n", apicid);
 		return -EINVAL;
 	}
-	if (vp_id > ms_hyperv.max_vp_index) {
-		pr_err("Invalid CPU id %d for APIC ID %d\n", vp_id, apicid);
+	if (vp_index > ms_hyperv.max_vp_index) {
+		pr_err("Invalid CPU id %d for APIC ID %d\n", vp_index, apicid);
 		return -EINVAL;
 	}
 
-	return hv_vtl_bringup_vcpu(vp_id, cpu, start_eip);
+	return hv_vtl_bringup_vcpu(vp_index, cpu, start_eip);
 }
 
 int __init hv_vtl_early_init(void)
diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index 77bf05f06b9e..0cc239cdb4da 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 <linux/cpu.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(u32 apic_id, unsigned long start_ip)
 {
 	struct sev_es_save_area *vmsa = (struct sev_es_save_area *)
 		__get_free_page(GFP_KERNEL | __GFP_ZERO);
@@ -297,10 +298,27 @@ int hv_snp_boot_ap(u32 cpu, unsigned long start_ip)
 	u64 ret, retry = 5;
 	struct hv_enable_vp_vtl *start_vp_input;
 	unsigned long flags;
+	int cpu, vp_index;
 
 	if (!vmsa)
 		return -ENOMEM;
 
+	/* Find the Hyper-V VP index which might be not the same as APIC ID */
+	vp_index = hv_apicid_to_vp_index(apic_id);
+	if (vp_index < 0 || vp_index > ms_hyperv.max_vp_index)
+		return -EINVAL;
+
+	/*
+	 * Find the Linux CPU number for addressing the per-CPU data, and it
+	 * might not be the same as APIC ID.
+	 */
+	for_each_present_cpu(cpu) {
+		if (arch_match_cpu_phys_id(cpu, apic_id))
+			break;
+	}
+	if (cpu >= nr_cpu_ids)
+		return -EINVAL;
+
 	native_store_gdt(&gdtr);
 
 	vmsa->gdtr.base = gdtr.address;
@@ -348,7 +366,7 @@ int hv_snp_boot_ap(u32 cpu, unsigned long start_ip)
 	start_vp_input = (struct hv_enable_vp_vtl *)ap_start_input_arg;
 	memset(start_vp_input, 0, sizeof(*start_vp_input));
 	start_vp_input->partition_id = -1;
-	start_vp_input->vp_index = cpu;
+	start_vp_input->vp_index = vp_index;
 	start_vp_input->target_vtl.target_vtl = ms_hyperv.vtl;
 	*(u64 *)&start_vp_input->vp_context = __pa(vmsa) | 1;