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

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>