powerpc/vas: Create take/drop pid and mm reference functions

Take pid and mm references when each window opens and drops during
close. This functionality is needed for powerNV and pseries. So
this patch defines the existing code as functions in common book3s
platform vas-api.c

Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/2fa40df962250a737c804e58202924717b39e381.camel@linux.ibm.com

arch/powerpc/include/asm/vas.h

@@ -5,6 +5,9 @@
 
 #ifndef _ASM_POWERPC_VAS_H
 #define _ASM_POWERPC_VAS_H
+#include <linux/sched/mm.h>
+#include <linux/mmu_context.h>
+#include <asm/icswx.h>
 #include <uapi/asm/vas-api.h>
 
 struct vas_window;
@@ -49,6 +52,17 @@ enum vas_cop_type {
 	VAS_COP_TYPE_MAX,
 };
 
+/*
+ * User space VAS windows are opened by tasks and take references
+ * to pid and mm until windows are closed.
+ * Stores pid, mm, and tgid for each window.
+ */
+struct vas_user_win_ref {
+	struct pid *pid;	/* PID of owner */
+	struct pid *tgid;	/* Thread group ID of owner */
+	struct mm_struct *mm;	/* Linux process mm_struct */
+};
+
 /*
  * User space window operations used for powernv and powerVM
  */
@@ -59,6 +73,31 @@ struct vas_user_win_ops {
 	int (*close_win)(struct vas_window *);
 };
 
+static inline void put_vas_user_win_ref(struct vas_user_win_ref *ref)
+{
+	/* Drop references to pid, tgid, and mm */
+	put_pid(ref->pid);
+	put_pid(ref->tgid);
+	if (ref->mm)
+		mmdrop(ref->mm);
+}
+
+static inline void vas_user_win_add_mm_context(struct vas_user_win_ref *ref)
+{
+	mm_context_add_vas_window(ref->mm);
+	/*
+	 * Even a process that has no foreign real address mapping can
+	 * use an unpaired COPY instruction (to no real effect). Issue
+	 * CP_ABORT to clear any pending COPY and prevent a covert
+	 * channel.
+	 *
+	 * __switch_to() will issue CP_ABORT on future context switches
+	 * if process / thread has any open VAS window (Use
+	 * current->mm->context.vas_windows).
+	 */
+	asm volatile(PPC_CP_ABORT);
+}
+
 /*
  * Receive window attributes specified by the (in-kernel) owner of window.
  */
@@ -190,4 +229,5 @@ int vas_register_coproc_api(struct module *mod, enum vas_cop_type cop_type,
 			    const struct vas_user_win_ops *vops);
 void vas_unregister_coproc_api(void);
 
+int get_vas_user_win_ref(struct vas_user_win_ref *task_ref);
 #endif /* __ASM_POWERPC_VAS_H */

arch/powerpc/platforms/book3s/vas-api.c

@@ -55,6 +55,45 @@ static char *coproc_devnode(struct device *dev, umode_t *mode)
 	return kasprintf(GFP_KERNEL, "crypto/%s", dev_name(dev));
 }
 
+/*
+ * Take reference to pid and mm
+ */
+int get_vas_user_win_ref(struct vas_user_win_ref *task_ref)
+{
+	/*
+	 * Window opened by a child thread may not be closed when
+	 * it exits. So take reference to its pid and release it
+	 * when the window is free by parent thread.
+	 * Acquire a reference to the task's pid to make sure
+	 * pid will not be re-used - needed only for multithread
+	 * applications.
+	 */
+	task_ref->pid = get_task_pid(current, PIDTYPE_PID);
+	/*
+	 * Acquire a reference to the task's mm.
+	 */
+	task_ref->mm = get_task_mm(current);
+	if (!task_ref->mm) {
+		put_pid(task_ref->pid);
+		pr_err("VAS: pid(%d): mm_struct is not found\n",
+				current->pid);
+		return -EPERM;
+	}
+
+	mmgrab(task_ref->mm);
+	mmput(task_ref->mm);
+	/*
+	 * Process closes window during exit. In the case of
+	 * multithread application, the child thread can open
+	 * window and can exit without closing it. So takes tgid
+	 * reference until window closed to make sure tgid is not
+	 * reused.
+	 */
+	task_ref->tgid = find_get_pid(task_tgid_vnr(current));
+
+	return 0;
+}
+
 static int coproc_open(struct inode *inode, struct file *fp)
 {
 	struct coproc_instance *cp_inst;

arch/powerpc/platforms/powernv/vas-fault.c

@@ -73,7 +73,7 @@ static void update_csb(struct vas_window *window,
 	 * NX user space windows can not be opened for task->mm=NULL
 	 * and faults will not be generated for kernel requests.
 	 */
-	if (WARN_ON_ONCE(!window->mm || !window->user_win))
+	if (WARN_ON_ONCE(!window->task_ref.mm || !window->user_win))
 		return;
 
 	csb_addr = (void __user *)be64_to_cpu(crb->csb_addr);
@@ -92,7 +92,7 @@ static void update_csb(struct vas_window *window,
 	csb.address = crb->stamp.nx.fault_storage_addr;
 	csb.flags = 0;
 
-	pid = window->pid;
+	pid = window->task_ref.pid;
 	tsk = get_pid_task(pid, PIDTYPE_PID);
 	/*
 	 * Process closes send window after all pending NX requests are
@@ -111,7 +111,7 @@ static void update_csb(struct vas_window *window,
 	 * a window and exits without closing it.
 	 */
 	if (!tsk) {
-		pid = window->tgid;
+		pid = window->task_ref.tgid;
 		tsk = get_pid_task(pid, PIDTYPE_PID);
 		/*
 		 * Parent thread (tgid) will be closing window when it
@@ -127,7 +127,7 @@ static void update_csb(struct vas_window *window,
 		return;
 	}
 
-	kthread_use_mm(window->mm);
+	kthread_use_mm(window->task_ref.mm);
 	rc = copy_to_user(csb_addr, &csb, sizeof(csb));
 	/*
 	 * User space polls on csb.flags (first byte). So add barrier
@@ -139,7 +139,7 @@ static void update_csb(struct vas_window *window,
 		smp_mb();
 		rc = copy_to_user(csb_addr, &csb, sizeof(u8));
 	}
-	kthread_unuse_mm(window->mm);
+	kthread_unuse_mm(window->task_ref.mm);
 	put_task_struct(tsk);
 
 	/* Success */

arch/powerpc/platforms/powernv/vas-window.c

@@ -1065,51 +1065,11 @@ struct vas_window *vas_tx_win_open(int vasid, enum vas_cop_type cop,
 			rc = -ENODEV;
 			goto free_window;
 		}
-
-		/*
-		 * Window opened by a child thread may not be closed when
-		 * it exits. So take reference to its pid and release it
-		 * when the window is free by parent thread.
-		 * Acquire a reference to the task's pid to make sure
-		 * pid will not be re-used - needed only for multithread
-		 * applications.
-		 */
-		txwin->pid = get_task_pid(current, PIDTYPE_PID);
-		/*
-		 * Acquire a reference to the task's mm.
-		 */
-		txwin->mm = get_task_mm(current);
-
-		if (!txwin->mm) {
-			put_pid(txwin->pid);
-			pr_err("VAS: pid(%d): mm_struct is not found\n",
-					current->pid);
-			rc = -EPERM;
+		rc = get_vas_user_win_ref(&txwin->task_ref);
+		if (rc)
 			goto free_window;
-		}
 
-		mmgrab(txwin->mm);
-		mmput(txwin->mm);
-		mm_context_add_vas_window(txwin->mm);
-		/*
-		 * Process closes window during exit. In the case of
-		 * multithread application, the child thread can open
-		 * window and can exit without closing it. so takes tgid
-		 * reference until window closed to make sure tgid is not
-		 * reused.
-		 */
-		txwin->tgid = find_get_pid(task_tgid_vnr(current));
-		/*
-		 * Even a process that has no foreign real address mapping can
-		 * use an unpaired COPY instruction (to no real effect). Issue
-		 * CP_ABORT to clear any pending COPY and prevent a covert
-		 * channel.
-		 *
-		 * __switch_to() will issue CP_ABORT on future context switches
-		 * if process / thread has any open VAS window (Use
-		 * current->mm->context.vas_windows).
-		 */
-		asm volatile(PPC_CP_ABORT);
+		vas_user_win_add_mm_context(&txwin->task_ref);
 	}
 
 	set_vinst_win(vinst, txwin);
@@ -1340,13 +1300,8 @@ int vas_win_close(struct vas_window *window)
 	/* if send window, drop reference to matching receive window */
 	if (window->tx_win) {
 		if (window->user_win) {
-			/* Drop references to pid. tgid and mm */
-			put_pid(window->pid);
-			put_pid(window->tgid);
-			if (window->mm) {
-				mm_context_remove_vas_window(window->mm);
-				mmdrop(window->mm);
-			}
+			put_vas_user_win_ref(&window->task_ref);
+			mm_context_remove_vas_window(window->task_ref.mm);
 		}
 		put_rx_win(window->rxwin);
 	}

arch/powerpc/platforms/powernv/vas.h

@@ -357,11 +357,9 @@ struct vas_window {
 	bool user_win;		/* True if user space window */
 	void *hvwc_map;		/* HV window context */
 	void *uwc_map;		/* OS/User window context */
-	struct pid *pid;	/* Linux process id of owner */
-	struct pid *tgid;	/* Thread group ID of owner */
-	struct mm_struct *mm;	/* Linux process mm_struct */
 	int wcreds_max;		/* Window credits */
 
+	struct vas_user_win_ref task_ref;
 	char *dbgname;
 	struct dentry *dbgdir;
 
@@ -443,7 +441,7 @@ extern void vas_win_paste_addr(struct vas_window *window, u64 *addr,
 
 static inline int vas_window_pid(struct vas_window *window)
 {
-	return pid_vnr(window->pid);
+	return pid_vnr(window->task_ref.pid);
 }
 
 static inline void vas_log_write(struct vas_window *win, char *name,