KVM: e500: perform hugepage check after looking up the PFN

e500 KVM tries to bypass __kvm_faultin_pfn() in order to map VM_PFNMAP
VMAs as huge pages. This is a Bad Idea because VM_PFNMAP VMAs could
become noncontiguous as a result of callsto remap_pfn_range().

Instead, use the already existing host PTE lookup to retrieve a
valid host-side mapping level after __kvm_faultin_pfn() has
returned. Then find the largest size that will satisfy the
guest's request while staying within a single host PTE.

Signed-off-by: Paolo Bonzini <[e-mail]>

arch/powerpc/kvm/e500_mmu_host.c

···
 	struct tlbe_ref *ref)
 {
 	struct kvm_memory_slot *slot;
-	unsigned long pfn = 0; /* silence GCC warning */
+	unsigned int psize;
+	unsigned long pfn;
 	struct page *page = NULL;
 	unsigned long hva;
-	int pfnmap = 0;
 	int tsize = BOOK3E_PAGESZ_4K;
 	int ret = 0;
 	unsigned long mmu_seq;
 	struct kvm *kvm = vcpu_e500->vcpu.kvm;
-	unsigned long tsize_pages = 0;
 	pte_t *ptep;
 	unsigned int wimg = 0;
 	pgd_t *pgdir;
···
 	slot = gfn_to_memslot(vcpu_e500->vcpu.kvm, gfn);
 	hva = gfn_to_hva_memslot(slot, gfn);
 
-	if (tlbsel == 1) {
-		struct vm_area_struct *vma;
-		mmap_read_lock(kvm->mm);
-
-		vma = find_vma(kvm->mm, hva);
-		if (vma && hva >= vma->vm_start &&
-		    (vma->vm_flags & VM_PFNMAP)) {
-			/*
-			 * This VMA is a physically contiguous region (e.g.
-			 * /dev/mem) that bypasses normal Linux page
-			 * management.  Find the overlap between the
-			 * vma and the memslot.
-			 */
-
-			unsigned long start, end;
-			unsigned long slot_start, slot_end;
-
-			pfnmap = 1;
-			writable = vma->vm_flags & VM_WRITE;
-
-			start = vma->vm_pgoff;
-			end = start +
-			      vma_pages(vma);
-
-			pfn = start + ((hva - vma->vm_start) >> PAGE_SHIFT);
-
-			slot_start = pfn - (gfn - slot->base_gfn);
-			slot_end = slot_start + slot->npages;
-
-			if (start < slot_start)
-				start = slot_start;
-			if (end > slot_end)
-				end = slot_end;
-
-			tsize = (gtlbe->mas1 & MAS1_TSIZE_MASK) >>
-				MAS1_TSIZE_SHIFT;
-
-			/*
-			 * e500 doesn't implement the lowest tsize bit,
-			 * or 1K pages.
-			 */
-			tsize = max(BOOK3E_PAGESZ_4K, tsize & ~1);
-
-			/*
-			 * Now find the largest tsize (up to what the guest
-			 * requested) that will cover gfn, stay within the
-			 * range, and for which gfn and pfn are mutually
-			 * aligned.
-			 */
-
-			for (; tsize > BOOK3E_PAGESZ_4K; tsize -= 2) {
-				unsigned long gfn_start, gfn_end;
-				tsize_pages = 1UL << (tsize - 2);
-
-				gfn_start = gfn & ~(tsize_pages - 1);
-				gfn_end = gfn_start + tsize_pages;
-
-				if (gfn_start + pfn - gfn < start)
-					continue;
-				if (gfn_end + pfn - gfn > end)
-					continue;
-				if ((gfn & (tsize_pages - 1)) !=
-				    (pfn & (tsize_pages - 1)))
-					continue;
-
-				gvaddr &= ~((tsize_pages << PAGE_SHIFT) - 1);
-				pfn &= ~(tsize_pages - 1);
-				break;
-			}
-		} else if (vma && hva >= vma->vm_start &&
-			   is_vm_hugetlb_page(vma)) {
-			unsigned long psize = vma_kernel_pagesize(vma);
-
-			tsize = (gtlbe->mas1 & MAS1_TSIZE_MASK) >>
-				MAS1_TSIZE_SHIFT;
-
-			/*
-			 * Take the largest page size that satisfies both host
-			 * and guest mapping
-			 */
-			tsize = min(__ilog2(psize) - 10, tsize);
-
-			/*
-			 * e500 doesn't implement the lowest tsize bit,
-			 * or 1K pages.
-			 */
-			tsize = max(BOOK3E_PAGESZ_4K, tsize & ~1);
-		}
-
-		mmap_read_unlock(kvm->mm);
-	}
-
-	if (likely(!pfnmap)) {
-		tsize_pages = 1UL << (tsize + 10 - PAGE_SHIFT);
-		pfn = __kvm_faultin_pfn(slot, gfn, FOLL_WRITE, &writable, &page);
-		if (is_error_noslot_pfn(pfn)) {
-			if (printk_ratelimit())
-				pr_err("%s: real page not found for gfn %lx\n",
-				       __func__, (long)gfn);
-			return -EINVAL;
-		}
-
-		/* Align guest and physical address to page map boundaries */
-		pfn &= ~(tsize_pages - 1);
-		gvaddr &= ~((tsize_pages << PAGE_SHIFT) - 1);
+	pfn = __kvm_faultin_pfn(slot, gfn, FOLL_WRITE, &writable, &page);
+	if (is_error_noslot_pfn(pfn)) {
+		if (printk_ratelimit())
+			pr_err("%s: real page not found for gfn %lx\n",
+			       __func__, (long)gfn);
+		return -EINVAL;
 	}
 
 	spin_lock(&kvm->mmu_lock);
···
 	 * can't run hence pfn won't change.
 	 */
 	local_irq_save(flags);
-	ptep = find_linux_pte(pgdir, hva, NULL, NULL);
+	ptep = find_linux_pte(pgdir, hva, NULL, &psize);
 	if (ptep) {
 		pte_t pte = READ_ONCE(*ptep);
 
···
 		}
 	}
 	local_irq_restore(flags);
+
+	if (psize && tlbsel == 1) {
+		unsigned long psize_pages, tsize_pages;
+		unsigned long start, end;
+		unsigned long slot_start, slot_end;
+
+		psize_pages = 1UL << (psize - PAGE_SHIFT);
+		start = pfn & ~(psize_pages - 1);
+		end = start + psize_pages;
+
+		slot_start = pfn - (gfn - slot->base_gfn);
+		slot_end = slot_start + slot->npages;
+
+		if (start < slot_start)
+			start = slot_start;
+		if (end > slot_end)
+			end = slot_end;
+
+		tsize = (gtlbe->mas1 & MAS1_TSIZE_MASK) >>
+			MAS1_TSIZE_SHIFT;
+
+		/*
+		 * Any page size that doesn't satisfy the host mapping
+		 * will fail the start and end tests.
+		 */
+		tsize = min(psize - PAGE_SHIFT + BOOK3E_PAGESZ_4K, tsize);
+
+		/*
+		 * e500 doesn't implement the lowest tsize bit,
+		 * or 1K pages.
+		 */
+		tsize = max(BOOK3E_PAGESZ_4K, tsize & ~1);
+
+		/*
+		 * Now find the largest tsize (up to what the guest
+		 * requested) that will cover gfn, stay within the
+		 * range, and for which gfn and pfn are mutually
+		 * aligned.
+		 */
+
+		for (; tsize > BOOK3E_PAGESZ_4K; tsize -= 2) {
+			unsigned long gfn_start, gfn_end;
+			tsize_pages = 1UL << (tsize - 2);
+
+			gfn_start = gfn & ~(tsize_pages - 1);
+			gfn_end = gfn_start + tsize_pages;
+
+			if (gfn_start + pfn - gfn < start)
+				continue;
+			if (gfn_end + pfn - gfn > end)
+				continue;
+			if ((gfn & (tsize_pages - 1)) !=
+			    (pfn & (tsize_pages - 1)))
+				continue;
+
+			gvaddr &= ~((tsize_pages << PAGE_SHIFT) - 1);
+			pfn &= ~(tsize_pages - 1);
+			break;
+		}
+	}
 
 	kvmppc_e500_ref_setup(ref, gtlbe, pfn, wimg, writable);
 	kvmppc_e500_setup_stlbe(&vcpu_e500->vcpu, gtlbe, tsize,