Re: [PATCH 28/39] mm: drop some redundant checks around hugetlb VMAs

Adjust code which inadvertently perform redundant checks on hugetlb VMAs
and clean them up:

* hugetlb VMAs have VMA_DONTEXPAND_BIT set so a VMA_SPECIAL_FLAGS check
  suffices. (migrate_vma_setup() regains an explicit hugetlb test later in
  the series, once VMA_SPECIAL_FLAGS is removed.)

* hugetlb VMAs unconditionally set vma->vm_ops, so they are never
  anonymous.

* hugetlb VMAs do not set VMA_PFNMAP_BIT so checking for this is redundant.

While we're here also drop a VM_BUG_ON() which the simplified check above
makes unreachable, and use the new VMA flag API.

No functional change intended.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 arch/arm64/kvm/mmu.c         | 4 +---
 drivers/gpu/drm/drm_gpusvm.c | 3 +--
 mm/migrate_device.c          | 4 ++--
 3 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index a7968f8d24bf..3c1240ffc38d 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c

@@ -1463,14 +1463,12 @@ static int get_vma_page_shift(struct vm_area_struct *vma, unsigned long hva)
 {
 	unsigned long pa;
 
-	if (vma_is_hugetlb(vma) && !(vma->vm_flags & VM_PFNMAP))
+	if (vma_is_hugetlb(vma))
 		return huge_page_shift(hstate_vma(vma));
 
 	if (!(vma->vm_flags & VM_PFNMAP))
 		return PAGE_SHIFT;
 
-	VM_BUG_ON(vma_is_hugetlb(vma));
-
 	pa = (vma->vm_pgoff << PAGE_SHIFT) + (hva - vma->vm_start);
 
 #ifndef __PAGETABLE_PMD_FOLDED