A vulnerability in the Linux kernel's x86 Hyper-V code was fixed by changing the use of per-CPU output pages in the hv_apicid_to_vp_index() function. The function previously used separate per-CPU input and output pages, but in some configurations (SEV-SNP CoCo VMs without a paravisor), the output page was not allocated, causing the hypervisor to write output to unallocated guest memory. The fix involves using the input page for both input and output to avoid unallocated memory access.