powerpc/vas: Move update_csb/dump_crb to common book3s platform

If a coprocessor encounters an error translating an address, the
VAS will cause an interrupt in the host. The kernel processes
the fault by updating CSB. This functionality is same for both
powerNV and pseries. So this patch moves these functions to
common vas-api.c and the actual functionality is not changed.

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/bf8d5b0770fa1ef5cba88c96580caa08d999d3b5.camel@linux.ibm.com

2 files changed, 176 insertions, 146 deletions

diff --git a/arch/powerpc/platforms/book3s/vas-api.c b/arch/powerpc/platforms/book3s/vas-api.c
index 4ce82500f4c5..30172e52e16b 100644
--- a/arch/powerpc/platforms/book3s/vas-api.c
+++ b/arch/powerpc/platforms/book3s/vas-api.c
@@ -10,6 +10,9 @@
 #include <linux/fs.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
+#include <linux/kthread.h>
+#include <linux/sched/signal.h>
+#include <linux/mmu_context.h>
 #include <linux/io.h>
 #include <asm/vas.h>
 #include <uapi/asm/vas-api.h>
@@ -94,6 +97,170 @@ int get_vas_user_win_ref(struct vas_user_win_ref *task_ref)
 	return 0;
 }
 
+/*
+ * Successful return must release the task reference with
+ * put_task_struct
+ */
+static bool ref_get_pid_and_task(struct vas_user_win_ref *task_ref,
+			  struct task_struct **tskp, struct pid **pidp)
+{
+	struct task_struct *tsk;
+	struct pid *pid;
+
+	pid = task_ref->pid;
+	tsk = get_pid_task(pid, PIDTYPE_PID);
+	if (!tsk) {
+		pid = task_ref->tgid;
+		tsk = get_pid_task(pid, PIDTYPE_PID);
+		/*
+		 * Parent thread (tgid) will be closing window when it
+		 * exits. So should not get here.
+		 */
+		if (WARN_ON_ONCE(!tsk))
+			return false;
+	}
+
+	/* Return if the task is exiting. */
+	if (tsk->flags & PF_EXITING) {
+		put_task_struct(tsk);
+		return false;
+	}
+
+	*tskp = tsk;
+	*pidp = pid;
+
+	return true;
+}
+
+/*
+ * Update the CSB to indicate a translation error.
+ *
+ * User space will be polling on CSB after the request is issued.
+ * If NX can handle the request without any issues, it updates CSB.
+ * Whereas if NX encounters page fault, the kernel will handle the
+ * fault and update CSB with translation error.
+ *
+ * If we are unable to update the CSB means copy_to_user failed due to
+ * invalid csb_addr, send a signal to the process.
+ */
+void vas_update_csb(struct coprocessor_request_block *crb,
+		    struct vas_user_win_ref *task_ref)
+{
+	struct coprocessor_status_block csb;
+	struct kernel_siginfo info;
+	struct task_struct *tsk;
+	void __user *csb_addr;
+	struct pid *pid;
+	int rc;
+
+	/*
+	 * 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(!task_ref->mm))
+		return;
+
+	csb_addr = (void __user *)be64_to_cpu(crb->csb_addr);
+
+	memset(&csb, 0, sizeof(csb));
+	csb.cc = CSB_CC_FAULT_ADDRESS;
+	csb.ce = CSB_CE_TERMINATION;
+	csb.cs = 0;
+	csb.count = 0;
+
+	/*
+	 * NX operates and returns in BE format as defined CRB struct.
+	 * So saves fault_storage_addr in BE as NX pastes in FIFO and
+	 * expects user space to convert to CPU format.
+	 */
+	csb.address = crb->stamp.nx.fault_storage_addr;
+	csb.flags = 0;
+
+	/*
+	 * Process closes send window after all pending NX requests are
+	 * completed. In multi-thread applications, a child thread can
+	 * open a window and can exit without closing it. May be some
+	 * requests are pending or this window can be used by other
+	 * threads later. We should handle faults if NX encounters
+	 * pages faults on these requests. Update CSB with translation
+	 * error and fault address. If csb_addr passed by user space is
+	 * invalid, send SEGV signal to pid saved in window. If the
+	 * child thread is not running, send the signal to tgid.
+	 * Parent thread (tgid) will close this window upon its exit.
+	 *
+	 * pid and mm references are taken when window is opened by
+	 * process (pid). So tgid is used only when child thread opens
+	 * a window and exits without closing it.
+	 */
+
+	if (!ref_get_pid_and_task(task_ref, &tsk, &pid))
+		return;
+
+	kthread_use_mm(task_ref->mm);
+	rc = copy_to_user(csb_addr, &csb, sizeof(csb));
+	/*
+	 * User space polls on csb.flags (first byte). So add barrier
+	 * then copy first byte with csb flags update.
+	 */
+	if (!rc) {
+		csb.flags = CSB_V;
+		/* Make sure update to csb.flags is visible now */
+		smp_mb();
+		rc = copy_to_user(csb_addr, &csb, sizeof(u8));
+	}
+	kthread_unuse_mm(task_ref->mm);
+	put_task_struct(tsk);
+
+	/* Success */
+	if (!rc)
+		return;
+
+
+	pr_debug("Invalid CSB address 0x%p signalling pid(%d)\n",
+			csb_addr, pid_vnr(pid));
+
+	clear_siginfo(&info);
+	info.si_signo = SIGSEGV;
+	info.si_errno = EFAULT;
+	info.si_code = SEGV_MAPERR;
+	info.si_addr = csb_addr;
+	/*
+	 * process will be polling on csb.flags after request is sent to
+	 * NX. So generally CSB update should not fail except when an
+	 * application passes invalid csb_addr. So an error message will
+	 * be displayed and leave it to user space whether to ignore or
+	 * handle this signal.
+	 */
+	rcu_read_lock();
+	rc = kill_pid_info(SIGSEGV, &info, pid);
+	rcu_read_unlock();
+
+	pr_devel("%s(): pid %d kill_proc_info() rc %d\n", __func__,
+			pid_vnr(pid), rc);
+}
+
+void vas_dump_crb(struct coprocessor_request_block *crb)
+{
+	struct data_descriptor_entry *dde;
+	struct nx_fault_stamp *nx;
+
+	dde = &crb->source;
+	pr_devel("SrcDDE: addr 0x%llx, len %d, count %d, idx %d, flags %d\n",
+		be64_to_cpu(dde->address), be32_to_cpu(dde->length),
+		dde->count, dde->index, dde->flags);
+
+	dde = &crb->target;
+	pr_devel("TgtDDE: addr 0x%llx, len %d, count %d, idx %d, flags %d\n",
+		be64_to_cpu(dde->address), be32_to_cpu(dde->length),
+		dde->count, dde->index, dde->flags);
+
+	nx = &crb->stamp.nx;
+	pr_devel("NX Stamp: PSWID 0x%x, FSA 0x%llx, flags 0x%x, FS 0x%x\n",
+		be32_to_cpu(nx->pswid),
+		be64_to_cpu(crb->stamp.nx.fault_storage_addr),
+		nx->flags, nx->fault_status);
+}
+
 static int coproc_open(struct inode *inode, struct file *fp)
 {
 	struct coproc_instance *cp_inst;
diff --git a/arch/powerpc/platforms/powernv/vas-fault.c b/arch/powerpc/platforms/powernv/vas-fault.c
index ac3a71ec3bd5..2729ac541fb3 100644
--- a/arch/powerpc/platforms/powernv/vas-fault.c
+++ b/arch/powerpc/platforms/powernv/vas-fault.c
@@ -26,150 +26,6 @@
  */
 #define VAS_FAULT_WIN_FIFO_SIZE	(4 << 20)
 
-static void dump_crb(struct coprocessor_request_block *crb)
-{
-	struct data_descriptor_entry *dde;
-	struct nx_fault_stamp *nx;
-
-	dde = &crb->source;
-	pr_devel("SrcDDE: addr 0x%llx, len %d, count %d, idx %d, flags %d\n",
-		be64_to_cpu(dde->address), be32_to_cpu(dde->length),
-		dde->count, dde->index, dde->flags);
-
-	dde = &crb->target;
-	pr_devel("TgtDDE: addr 0x%llx, len %d, count %d, idx %d, flags %d\n",
-		be64_to_cpu(dde->address), be32_to_cpu(dde->length),
-		dde->count, dde->index, dde->flags);
-
-	nx = &crb->stamp.nx;
-	pr_devel("NX Stamp: PSWID 0x%x, FSA 0x%llx, flags 0x%x, FS 0x%x\n",
-		be32_to_cpu(nx->pswid),
-		be64_to_cpu(crb->stamp.nx.fault_storage_addr),
-		nx->flags, nx->fault_status);
-}
-
-/*
- * Update the CSB to indicate a translation error.
- *
- * User space will be polling on CSB after the request is issued.
- * If NX can handle the request without any issues, it updates CSB.
- * Whereas if NX encounters page fault, the kernel will handle the
- * fault and update CSB with translation error.
- *
- * If we are unable to update the CSB means copy_to_user failed due to
- * invalid csb_addr, send a signal to the process.
- */
-static void update_csb(struct vas_window *window,
-			struct coprocessor_request_block *crb)
-{
-	struct coprocessor_status_block csb;
-	struct kernel_siginfo info;
-	struct task_struct *tsk;
-	void __user *csb_addr;
-	struct pid *pid;
-	int rc;
-
-	/*
-	 * 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->task_ref.mm || !window->user_win))
-		return;
-
-	csb_addr = (void __user *)be64_to_cpu(crb->csb_addr);
-
-	memset(&csb, 0, sizeof(csb));
-	csb.cc = CSB_CC_FAULT_ADDRESS;
-	csb.ce = CSB_CE_TERMINATION;
-	csb.cs = 0;
-	csb.count = 0;
-
-	/*
-	 * NX operates and returns in BE format as defined CRB struct.
-	 * So saves fault_storage_addr in BE as NX pastes in FIFO and
-	 * expects user space to convert to CPU format.
-	 */
-	csb.address = crb->stamp.nx.fault_storage_addr;
-	csb.flags = 0;
-
-	pid = window->task_ref.pid;
-	tsk = get_pid_task(pid, PIDTYPE_PID);
-	/*
-	 * Process closes send window after all pending NX requests are
-	 * completed. In multi-thread applications, a child thread can
-	 * open a window and can exit without closing it. May be some
-	 * requests are pending or this window can be used by other
-	 * threads later. We should handle faults if NX encounters
-	 * pages faults on these requests. Update CSB with translation
-	 * error and fault address. If csb_addr passed by user space is
-	 * invalid, send SEGV signal to pid saved in window. If the
-	 * child thread is not running, send the signal to tgid.
-	 * Parent thread (tgid) will close this window upon its exit.
-	 *
-	 * pid and mm references are taken when window is opened by
-	 * process (pid). So tgid is used only when child thread opens
-	 * a window and exits without closing it.
-	 */
-	if (!tsk) {
-		pid = window->task_ref.tgid;
-		tsk = get_pid_task(pid, PIDTYPE_PID);
-		/*
-		 * Parent thread (tgid) will be closing window when it
-		 * exits. So should not get here.
-		 */
-		if (WARN_ON_ONCE(!tsk))
-			return;
-	}
-
-	/* Return if the task is exiting. */
-	if (tsk->flags & PF_EXITING) {
-		put_task_struct(tsk);
-		return;
-	}
-
-	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
-	 * then copy first byte with csb flags update.
-	 */
-	if (!rc) {
-		csb.flags = CSB_V;
-		/* Make sure update to csb.flags is visible now */
-		smp_mb();
-		rc = copy_to_user(csb_addr, &csb, sizeof(u8));
-	}
-	kthread_unuse_mm(window->task_ref.mm);
-	put_task_struct(tsk);
-
-	/* Success */
-	if (!rc)
-		return;
-
-	pr_debug("Invalid CSB address 0x%p signalling pid(%d)\n",
-			csb_addr, pid_vnr(pid));
-
-	clear_siginfo(&info);
-	info.si_signo = SIGSEGV;
-	info.si_errno = EFAULT;
-	info.si_code = SEGV_MAPERR;
-	info.si_addr = csb_addr;
-
-	/*
-	 * process will be polling on csb.flags after request is sent to
-	 * NX. So generally CSB update should not fail except when an
-	 * application passes invalid csb_addr. So an error message will
-	 * be displayed and leave it to user space whether to ignore or
-	 * handle this signal.
-	 */
-	rcu_read_lock();
-	rc = kill_pid_info(SIGSEGV, &info, pid);
-	rcu_read_unlock();
-
-	pr_devel("%s(): pid %d kill_proc_info() rc %d\n", __func__,
-			pid_vnr(pid), rc);
-}
-
 static void dump_fifo(struct vas_instance *vinst, void *entry)
 {
 	unsigned long *end = vinst->fault_fifo + vinst->fault_fifo_size;
@@ -272,7 +128,7 @@ irqreturn_t vas_fault_thread_fn(int irq, void *data)
 				vinst->vas_id, vinst->fault_fifo, fifo,
 				vinst->fault_crbs);
 
-		dump_crb(crb);
+		vas_dump_crb(crb);
 		window = vas_pswid_to_window(vinst,
 				be32_to_cpu(crb->stamp.nx.pswid));
 
@@ -293,7 +149,14 @@ irqreturn_t vas_fault_thread_fn(int irq, void *data)
 
 			WARN_ON_ONCE(1);
 		} else {
-			update_csb(window, crb);
+			/*
+			 * NX sees faults only with user space windows.
+			 */
+			if (window->user_win)
+				vas_update_csb(crb, &window->task_ref);
+			else
+				WARN_ON_ONCE(!window->user_win);
+
 			/*
 			 * Return credit for send window after processing
 			 * fault CRB.