um: Abandon the _PAGE_NEWPROT bit

When a PTE is updated in the page table, the _PAGE_NEWPAGE bit will
always be set. And the corresponding page will always be mapped or
unmapped depending on whether the PTE is present or not. The check
on the _PAGE_NEWPROT bit is not really reachable. Abandoning it will
allow us to simplify the code and remove the unreachable code.

Reviewed-by: Benjamin Berg <[e-mail]>
Signed-off-by: Tiwei Bie <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Johannes Berg <[e-mail]>

arch/um/include/asm/pgtable.h

···
 
 #define _PAGE_PRESENT	0x001
 #define _PAGE_NEWPAGE	0x002
-#define _PAGE_NEWPROT	0x004
 #define _PAGE_RW	0x020
 #define _PAGE_USER	0x040
 #define _PAGE_ACCESSED	0x080
···
 	return pte_get_bits(pte, _PAGE_NEWPAGE);
 }
 
-static inline int pte_newprot(pte_t pte)
-{
-	return(pte_present(pte) && (pte_get_bits(pte, _PAGE_NEWPROT)));
-}
-
 /*
  * =================================
  * Flags setting section.
  * =================================
  */
-
-static inline pte_t pte_mknewprot(pte_t pte)
-{
-	pte_set_bits(pte, _PAGE_NEWPROT);
-	return(pte);
-}
 
 static inline pte_t pte_mkclean(pte_t pte)
 {
···
 
 static inline pte_t pte_wrprotect(pte_t pte)
 {
-	if (likely(pte_get_bits(pte, _PAGE_RW)))
-		pte_clear_bits(pte, _PAGE_RW);
-	else
-		return pte;
-	return(pte_mknewprot(pte));
+	pte_clear_bits(pte, _PAGE_RW);
+	return pte;
 }
 
 static inline pte_t pte_mkread(pte_t pte)
 {
-	if (unlikely(pte_get_bits(pte, _PAGE_USER)))
-		return pte;
 	pte_set_bits(pte, _PAGE_USER);
-	return(pte_mknewprot(pte));
+	return pte;
 }
 
 static inline pte_t pte_mkdirty(pte_t pte)
···
 
 static inline pte_t pte_mkwrite_novma(pte_t pte)
 {
-	if (unlikely(pte_get_bits(pte,  _PAGE_RW)))
-		return pte;
 	pte_set_bits(pte, _PAGE_RW);
-	return(pte_mknewprot(pte));
+	return pte;
 }
 
 static inline pte_t pte_mkuptodate(pte_t pte)
 {
 	pte_clear_bits(pte, _PAGE_NEWPAGE);
-	if(pte_present(pte))
-		pte_clear_bits(pte, _PAGE_NEWPROT);
-	return(pte);
+	return pte;
 }
 
 static inline pte_t pte_mknewpage(pte_t pte)
···
 	pte_copy(*pteptr, pteval);
 
 	/* If it's a swap entry, it needs to be marked _PAGE_NEWPAGE so
-	 * fix_range knows to unmap it.  _PAGE_NEWPROT is specific to
-	 * mapped pages.
+	 * update_pte_range knows to unmap it.
 	 */
 
 	*pteptr = pte_mknewpage(*pteptr);
-	if(pte_present(*pteptr)) *pteptr = pte_mknewprot(*pteptr);
 }
 
 #define PFN_PTE_SHIFT		PAGE_SHIFT
···
 	({ pte_t pte;					\
 							\
 	pte_set_val(pte, page_to_phys(page), (pgprot));	\
-	if (pte_present(pte))				\
-		pte_mknewprot(pte_mknewpage(pte));	\
 	pte;})
 
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)

arch/um/include/asm/tlbflush.h

···
 #include <linux/mm.h>
 
 /*
- * In UML, we need to sync the TLB over by using mmap/munmap/mprotect syscalls
- * from the process handling the MM (which can be the kernel itself).
+ * In UML, we need to sync the TLB over by using mmap/munmap syscalls from
+ * the process handling the MM (which can be the kernel itself).
  *
  * To track updates, we can hook into set_ptes and flush_tlb_*. With set_ptes
  * we catch all PTE transitions where memory that was unusable becomes usable.

arch/um/include/shared/os.h

···
 	unsigned long len, int prot, int phys_fd,
 	unsigned long long offset);
 int unmap(struct mm_id *mm_idp, unsigned long addr, unsigned long len);
-int protect(struct mm_id *mm_idp, unsigned long addr,
-	    unsigned long len, unsigned int prot);
 
 /* skas/process.c */
 extern int is_skas_winch(int pid, int fd, void *data);

arch/um/include/shared/skas/stub-data.h

···
 	STUB_SYSCALL_UNSET = 0,
 	STUB_SYSCALL_MMAP,
 	STUB_SYSCALL_MUNMAP,
-	STUB_SYSCALL_MPROTECT,
 };
 
 struct stub_syscall {

arch/um/kernel/skas/stub.c

···
 				return -1;
 			}
 			break;
-		case STUB_SYSCALL_MPROTECT:
-			res = stub_syscall3(__NR_mprotect,
-					    sc->mem.addr, sc->mem.length,
-					    sc->mem.prot);
-			if (res) {
-				d->err = res;
-				d->syscall_data_len = i;
-				return -1;
-			}
-			break;
 		default:
 			d->err = -95; /* EOPNOTSUPP */
 			d->syscall_data_len = i;

arch/um/kernel/tlb.c

···
 		    int phys_fd, unsigned long long offset);
 	int (*unmap)(struct mm_id *mm_idp,
 		     unsigned long virt, unsigned long len);
-	int (*mprotect)(struct mm_id *mm_idp,
-			unsigned long virt, unsigned long len,
-			unsigned int prot);
 };
 
 static int kern_map(struct mm_id *mm_idp,
···
 	return os_unmap_memory((void *)virt, len);
 }
 
-static int kern_mprotect(struct mm_id *mm_idp,
-			 unsigned long virt, unsigned long len,
-			 unsigned int prot)
-{
-	return os_protect_memory((void *)virt, len,
-				 prot & UM_PROT_READ, prot & UM_PROT_WRITE,
-				 1);
-}
-
 void report_enomem(void)
 {
 	printk(KERN_ERR "UML ran out of memory on the host side! "
···
 				   struct vm_ops *ops)
 {
 	pte_t *pte;
-	int r, w, x, prot, ret = 0;
+	int ret = 0;
 
 	pte = pte_offset_kernel(pmd, addr);
 	do {
-		r = pte_read(*pte);
-		w = pte_write(*pte);
-		x = pte_exec(*pte);
-		if (!pte_young(*pte)) {
-			r = 0;
-			w = 0;
-		} else if (!pte_dirty(*pte))
-			w = 0;
+		if (!pte_newpage(*pte))
+			continue;
 
-		prot = ((r ? UM_PROT_READ : 0) | (w ? UM_PROT_WRITE : 0) |
-			(x ? UM_PROT_EXEC : 0));
-		if (pte_newpage(*pte)) {
-			if (pte_present(*pte)) {
-				__u64 offset;
-				unsigned long phys = pte_val(*pte) & PAGE_MASK;
-				int fd = phys_mapping(phys, &offset);
+		if (pte_present(*pte)) {
+			__u64 offset;
+			unsigned long phys = pte_val(*pte) & PAGE_MASK;
+			int fd = phys_mapping(phys, &offset);
+			int r, w, x, prot;
 
-				ret = ops->mmap(ops->mm_idp, addr, PAGE_SIZE,
-						prot, fd, offset);
-			} else
-				ret = ops->unmap(ops->mm_idp, addr, PAGE_SIZE);
-		} else if (pte_newprot(*pte))
-			ret = ops->mprotect(ops->mm_idp, addr, PAGE_SIZE, prot);
+			r = pte_read(*pte);
+			w = pte_write(*pte);
+			x = pte_exec(*pte);
+			if (!pte_young(*pte)) {
+				r = 0;
+				w = 0;
+			} else if (!pte_dirty(*pte))
+				w = 0;
+
+			prot = (r ? UM_PROT_READ : 0) |
+			       (w ? UM_PROT_WRITE : 0) |
+			       (x ? UM_PROT_EXEC : 0);
+
+			ret = ops->mmap(ops->mm_idp, addr, PAGE_SIZE,
+					prot, fd, offset);
+		} else
+			ret = ops->unmap(ops->mm_idp, addr, PAGE_SIZE);
+
 		*pte = pte_mkuptodate(*pte);
 	} while (pte++, addr += PAGE_SIZE, ((addr < end) && !ret));
 	return ret;
···
 	if (mm == &init_mm) {
 		ops.mmap = kern_map;
 		ops.unmap = kern_unmap;
-		ops.mprotect = kern_mprotect;
 	} else {
 		ops.mmap = map;
 		ops.unmap = unmap;
-		ops.mprotect = protect;
 	}
 
 	pgd = pgd_offset(mm, addr);

arch/um/os-Linux/skas/mem.c

···
 
 	return 0;
 }
-
-int protect(struct mm_id *mm_idp, unsigned long addr, unsigned long len,
-	    unsigned int prot)
-{
-	struct stub_syscall *sc;
-
-	/* Compress with previous syscall if that is possible */
-	sc = syscall_stub_get_previous(mm_idp, STUB_SYSCALL_MPROTECT, addr);
-	if (sc && sc->mem.prot == prot) {
-		sc->mem.length += len;
-		return 0;
-	}
-
-	sc = syscall_stub_alloc(mm_idp);
-	sc->syscall = STUB_SYSCALL_MPROTECT;
-	sc->mem.addr = addr;
-	sc->mem.length = len;
-	sc->mem.prot = prot;
-
-	return 0;
-}