KVM: Use vCPU specific memslots in __kvm_vcpu_map()

When establishing a "host access map", lookup the gfn in the vCPU specific
memslots, as the intent is that the mapping will be established for the
current vCPU context.  Specifically, using __kvm_vcpu_map() in x86's SMM
context should create mappings based on the SMM memslots, not the non-SMM
memslots.

Luckily, the bug is benign as x86 is the only architecture with multiple
memslot address spaces, and all of x86's usage is limited to non-SMM.  The
calls in (or reachable by) {svm,vmx}_enter_smm() are made before
enter_smm() sets HF_SMM_MASK, and the calls in {svm,vmx}_leave_smm() are
made after emulator_leave_smm() clears HF_SMM_MASK.

Note, kvm_vcpu_unmap() uses the vCPU specific memslots, only the map() side
of things is broken.

Fixes: 357a18ad23 ("KVM: Kill kvm_map_gfn() / kvm_unmap_gfn() and gfn_to_pfn_cache")
Link: https://patch.msgid.link/20251121223444.355422-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

virt/kvm/kvm_main.c

@@ -3134,7 +3134,7 @@ int __kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *map,
 		   bool writable)
 {
 	struct kvm_follow_pfn kfp = {
-		.slot = gfn_to_memslot(vcpu->kvm, gfn),
+		.slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn),
 		.gfn = gfn,
 		.flags = writable ? FOLL_WRITE : 0,
 		.refcounted_page = &map->pinned_page,