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>

1 files changed, 33 insertions, 0 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);