KVM: PPC: Book3S HV: Use __gfn_to_pfn_memslot() in page fault handler

This changes the hypervisor page fault handler for radix guests to use
the generic KVM __gfn_to_pfn_memslot() function instead of using
get_user_pages_fast() and then handling the case of VM_PFNMAP vmas
specially.  The old code missed the case of VM_IO vmas; with this
change, VM_IO vmas will now be handled correctly by code within
__gfn_to_pfn_memslot.

Currently, __gfn_to_pfn_memslot calls hva_to_pfn, which only uses
__get_user_pages_fast for the initial lookup in the cases where
either atomic or async is set.  Since we are not setting either
atomic or async, we do our own __get_user_pages_fast first, for now.

This also adds code to check for the KVM_MEM_READONLY flag on the
memslot.  If it is set and this is a write access, we synthesize a
data storage interrupt for the guest.

In the case where the page is not normal RAM (i.e. page == NULL in
kvmppc_book3s_radix_page_fault(), we read the PTE from the Linux page
tables because we need the mapping attribute bits as well as the PFN.
(The mapping attribute bits indicate whether accesses have to be
non-cacheable and/or guarded.)
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_64_mmu_radix.c

@@ -392,11 +392,11 @@ int kvmppc_book3s_radix_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	unsigned long mmu_seq, pte_size;
 	unsigned long gpa, gfn, hva, pfn;
 	struct kvm_memory_slot *memslot;
-	struct page *page = NULL, *pages[1];
-	long ret, npages;
-	unsigned int writing;
-	struct vm_area_struct *vma;
-	unsigned long flags;
+	struct page *page = NULL;
+	long ret;
+	bool writing;
+	bool upgrade_write = false;
+	bool *upgrade_p = &upgrade_write;
 	pte_t pte, *ptep;
 	unsigned long pgflags;
 	unsigned int shift, level;
@@ -436,12 +436,17 @@ int kvmppc_book3s_radix_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 					      dsisr & DSISR_ISSTORE);
 	}
 
-	/* used to check for invalidations in progress */
-	mmu_seq = kvm->mmu_notifier_seq;
-	smp_rmb();
-
 	writing = (dsisr & DSISR_ISSTORE) != 0;
-	hva = gfn_to_hva_memslot(memslot, gfn);
+	if (memslot->flags & KVM_MEM_READONLY) {
+		if (writing) {
+			/* give the guest a DSI */
+			dsisr = DSISR_ISSTORE | DSISR_PROTFAULT;
+			kvmppc_core_queue_data_storage(vcpu, ea, dsisr);
+			return RESUME_GUEST;
+		}
+		upgrade_p = NULL;
+	}
+
 	if (dsisr & DSISR_SET_RC) {
 		/*
 		 * Need to set an R or C bit in the 2nd-level tables;
@@ -470,31 +475,38 @@ int kvmppc_book3s_radix_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 			return RESUME_GUEST;
 	}
 
-	ret = -EFAULT;
-	pfn = 0;
-	pte_size = PAGE_SIZE;
-	pgflags = _PAGE_READ | _PAGE_EXEC;
-	level = 0;
-	npages = get_user_pages_fast(hva, 1, writing, pages);
-	if (npages < 1) {
-		/* Check if it's an I/O mapping */
-		down_read(&current->mm->mmap_sem);
-		vma = find_vma(current->mm, hva);
-		if (vma && vma->vm_start <= hva && hva < vma->vm_end &&
-		    (vma->vm_flags & VM_PFNMAP)) {
-			pfn = vma->vm_pgoff +
-				((hva - vma->vm_start) >> PAGE_SHIFT);
-			pgflags = pgprot_val(vma->vm_page_prot);
-		}
-		up_read(&current->mm->mmap_sem);
-		if (!pfn)
-			return -EFAULT;
-	} else {
-		page = pages[0];
+	/* used to check for invalidations in progress */
+	mmu_seq = kvm->mmu_notifier_seq;
+	smp_rmb();
+
+	/*
+	 * Do a fast check first, since __gfn_to_pfn_memslot doesn't
+	 * do it with !atomic && !async, which is how we call it.
+	 * We always ask for write permission since the common case
+	 * is that the page is writable.
+	 */
+	hva = gfn_to_hva_memslot(memslot, gfn);
+	if (upgrade_p && __get_user_pages_fast(hva, 1, 1, &page) == 1) {
 		pfn = page_to_pfn(page);
-		if (PageCompound(page)) {
-			pte_size <<= compound_order(compound_head(page));
+		upgrade_write = true;
+	} else {
+		/* Call KVM generic code to do the slow-path check */
+		pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
+					   writing, upgrade_p);
+		if (is_error_noslot_pfn(pfn))
+			return -EFAULT;
+		page = NULL;
+		if (pfn_valid(pfn)) {
+			page = pfn_to_page(pfn);
+			if (PageReserved(page))
+				page = NULL;
+		}
+	}
+
 	/* See if we can insert a 1GB or 2MB large PTE here */
+	level = 0;
+	if (page && PageCompound(page)) {
+		pte_size = PAGE_SIZE << compound_order(compound_head(page));
 		if (pte_size >= PUD_SIZE &&
 		    (gpa & (PUD_SIZE - PAGE_SIZE)) ==
 		    (hva & (PUD_SIZE - PAGE_SIZE))) {
@@ -507,32 +519,48 @@ int kvmppc_book3s_radix_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 			pfn &= ~((PMD_SIZE >> PAGE_SHIFT) - 1);
 		}
 	}
-		/* See if we can provide write access */
-		if (writing) {
-			pgflags |= _PAGE_WRITE;
-		} else {
-			local_irq_save(flags);
-			ptep = find_current_mm_pte(current->mm->pgd,
-						   hva, NULL, NULL);
-			if (ptep && pte_write(*ptep))
-				pgflags |= _PAGE_WRITE;
-			local_irq_restore(flags);
-		}
-	}
 
 	/*
 	 * Compute the PTE value that we need to insert.
 	 */
-	pgflags |= _PAGE_PRESENT | _PAGE_PTE | _PAGE_ACCESSED;
-	if (pgflags & _PAGE_WRITE)
-		pgflags |= _PAGE_DIRTY;
+	if (page) {
+		pgflags = _PAGE_READ | _PAGE_EXEC | _PAGE_PRESENT | _PAGE_PTE |
+			_PAGE_ACCESSED;
+		if (writing || upgrade_write)
+			pgflags |= _PAGE_WRITE | _PAGE_DIRTY;
 		pte = pfn_pte(pfn, __pgprot(pgflags));
+	} else {
+		/*
+		 * Read the PTE from the process' radix tree and use that
+		 * so we get the attribute bits.
+		 */
+		local_irq_disable();
+		ptep = __find_linux_pte(vcpu->arch.pgdir, hva, NULL, &shift);
+		pte = *ptep;
+		local_irq_enable();
+		if (shift == PUD_SHIFT &&
+		    (gpa & (PUD_SIZE - PAGE_SIZE)) ==
+		    (hva & (PUD_SIZE - PAGE_SIZE))) {
+			level = 2;
+		} else if (shift == PMD_SHIFT &&
+			   (gpa & (PMD_SIZE - PAGE_SIZE)) ==
+			   (hva & (PMD_SIZE - PAGE_SIZE))) {
+			level = 1;
+		} else if (shift && shift != PAGE_SHIFT) {
+			/* Adjust PFN */
+			unsigned long mask = (1ul << shift) - PAGE_SIZE;
+			pte = __pte(pte_val(pte) | (hva & mask));
+		}
+		if (!(writing || upgrade_write))
+			pte = __pte(pte_val(pte) & ~ _PAGE_WRITE);
+		pte = __pte(pte_val(pte) | _PAGE_EXEC);
+	}
 
 	/* Allocate space in the tree and write the PTE */
 	ret = kvmppc_create_pte(kvm, pte, gpa, level, mmu_seq);
 
 	if (page) {
-		if (!ret && (pgflags & _PAGE_WRITE))
+		if (!ret && (pte_val(pte) & _PAGE_WRITE))
 			set_page_dirty_lock(page);
 		put_page(page);
 	}