KVM: VMX: Initialize vmcs01.VM_EXIT_MSR_STORE_ADDR with list address

Initialize vmcs01.VM_EXIT_MSR_STORE_ADDR to point at the vCPU's
msr_autostore list in anticipation of utilizing the auto-store
functionality, and to harden KVM against stray reads to pfn 0 (or, in
theory, a random pfn if the underlying CPU uses a complex scheme for
encoding VMCS data).  The MSR auto lists are supposed to be ignored if the
associated COUNT VMCS field is '0', but leaving the ADDR field
zero-initialized in memory is an unnecessary risk (albeit a minuscule risk)
given that the cost is a single VMWRITE during vCPU creation.

Tested-by: Manali Shukla <manali.shukla@amd.com>
Link: https://patch.msgid.link/20251206001720.468579-44-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/vmx/vmx.c

@@ -4933,6 +4933,7 @@ static void init_vmcs(struct vcpu_vmx *vmx)
 		vmcs_write64(VM_FUNCTION_CONTROL, 0);
 
 	vmcs_write32(VM_EXIT_MSR_STORE_COUNT, 0);
+	vmcs_write64(VM_EXIT_MSR_STORE_ADDR, __pa(vmx->msr_autostore.val));
 	vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, 0);
 	vmcs_write64(VM_EXIT_MSR_LOAD_ADDR, __pa(vmx->msr_autoload.host.val));
 	vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, 0);