KVM: arm64: Assume non-PFNMAP/MIXEDMAP VMAs can be mapped cacheable

Despite its name, kvm_is_device_pfn() is actually used to determine if a
given PFN has a kernel mapping that can be used to perform cache
maintenance, as it calls pfn_is_map_memory() internally.

Expand the helper into its single callsite and further condition the
check on the VMA having either VM_PFNMAP or VM_MIXEDMAP set. VMAs that
set neither of these flags must always contain Normal, struct page
backed memory with valid aliases in the kernel address space.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Tested-by: Donald Dutile <ddutile@redhat.com>
Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20250705071717.5062-3-ankita@nvidia.com
[ Oliver: fixed typos, refined changelog ]
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: ankita-nv

arch/arm64/kvm/mmu.c

@@ -193,11 +193,6 @@ int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm,
 	return 0;
 }
 
-static bool kvm_is_device_pfn(unsigned long pfn)
-{
-	return !pfn_is_map_memory(pfn);
-}
-
 static void *stage2_memcache_zalloc_page(void *arg)
 {
 	struct kvm_mmu_memory_cache *mc = arg;
@@ -1492,6 +1487,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R;
 	struct kvm_pgtable *pgt;
 	struct page *page;
+	vm_flags_t vm_flags;
 	enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_HANDLE_FAULT | KVM_PGTABLE_WALK_SHARED;
 
 	if (fault_is_perm)
@@ -1619,6 +1615,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 
 	vfio_allow_any_uc = vma->vm_flags & VM_ALLOW_ANY_UNCACHED;
 
+	vm_flags = vma->vm_flags;
+
 	/* Don't use the VMA after the unlock -- it may have vanished */
 	vma = NULL;
 
@@ -1642,7 +1640,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	if (is_error_noslot_pfn(pfn))
 		return -EFAULT;
 
-	if (kvm_is_device_pfn(pfn)) {
+	if (vm_flags & (VM_PFNMAP | VM_MIXEDMAP) && !pfn_is_map_memory(pfn)) {
 		/*
 		 * If the page was identified as device early by looking at
 		 * the VMA flags, vma_pagesize is already representing the