1 files changed, 382 insertions, 0 deletions
diff --git a/arch/powerpc/platforms/powernv/vas-fault.c b/arch/powerpc/platforms/powernv/vas-fault.c
new file mode 100644
index 000000000..dd9c23c09
--- /dev/null
+++ b/arch/powerpc/platforms/powernv/vas-fault.c
@@ -0,0 +1,382 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * VAS Fault handling.
+ * Copyright 2019, IBM Corporation
+ */
+
+#define pr_fmt(fmt) "vas: " fmt
+
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/kthread.h>
+#include <linux/sched/signal.h>
+#include <linux/mmu_context.h>
+#include <asm/icswx.h>
+
+#include "vas.h"
+
+/*
+ * The maximum FIFO size for fault window can be 8MB
+ * (VAS_RX_FIFO_SIZE_MAX). Using 4MB FIFO since each VAS
+ * instance will be having fault window.
+ * 8MB FIFO can be used if expects more faults for each VAS
+ * instance.
+ */
+#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->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->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->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->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->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;
+	unsigned long *fifo = entry;
+	int i;
+
+	pr_err("Fault fifo size %d, Max crbs %d\n", vinst->fault_fifo_size,
+			vinst->fault_fifo_size / CRB_SIZE);
+
+	/* Dump 10 CRB entries or until end of FIFO */
+	pr_err("Fault FIFO Dump:\n");
+	for (i = 0; i < 10*(CRB_SIZE/8) && fifo < end; i += 4, fifo += 4) {
+		pr_err("[%.3d, %p]: 0x%.16lx 0x%.16lx 0x%.16lx 0x%.16lx\n",
+			i, fifo, *fifo, *(fifo+1), *(fifo+2), *(fifo+3));
+	}
+}
+
+/*
+ * Process valid CRBs in fault FIFO.
+ * NX process user space requests, return credit and update the status
+ * in CRB. If it encounters transalation error when accessing CRB or
+ * request buffers, raises interrupt on the CPU to handle the fault.
+ * It takes credit on fault window, updates nx_fault_stamp in CRB with
+ * the following information and pastes CRB in fault FIFO.
+ *
+ * pswid - window ID of the window on which the request is sent.
+ * fault_storage_addr - fault address
+ *
+ * It can raise a single interrupt for multiple faults. Expects OS to
+ * process all valid faults and return credit for each fault on user
+ * space and fault windows. This fault FIFO control will be done with
+ * credit mechanism. NX can continuously paste CRBs until credits are not
+ * available on fault window. Otherwise, returns with RMA_reject.
+ *
+ * Total credits available on fault window: FIFO_SIZE(4MB)/CRBS_SIZE(128)
+ *
+ */
+irqreturn_t vas_fault_thread_fn(int irq, void *data)
+{
+	struct vas_instance *vinst = data;
+	struct coprocessor_request_block *crb, *entry;
+	struct coprocessor_request_block buf;
+	struct vas_window *window;
+	unsigned long flags;
+	void *fifo;
+
+	crb = &buf;
+
+	/*
+	 * VAS can interrupt with multiple page faults. So process all
+	 * valid CRBs within fault FIFO until reaches invalid CRB.
+	 * We use CCW[0] and pswid to validate validate CRBs:
+	 *
+	 * CCW[0]	Reserved bit. When NX pastes CRB, CCW[0]=0
+	 *		OS sets this bit to 1 after reading CRB.
+	 * pswid	NX assigns window ID. Set pswid to -1 after
+	 *		reading CRB from fault FIFO.
+	 *
+	 * We exit this function if no valid CRBs are available to process.
+	 * So acquire fault_lock and reset fifo_in_progress to 0 before
+	 * exit.
+	 * In case kernel receives another interrupt with different page
+	 * fault, interrupt handler returns with IRQ_HANDLED if
+	 * fifo_in_progress is set. Means these new faults will be
+	 * handled by the current thread. Otherwise set fifo_in_progress
+	 * and return IRQ_WAKE_THREAD to wake up thread.
+	 */
+	while (true) {
+		spin_lock_irqsave(&vinst->fault_lock, flags);
+		/*
+		 * Advance the fault fifo pointer to next CRB.
+		 * Use CRB_SIZE rather than sizeof(*crb) since the latter is
+		 * aligned to CRB_ALIGN (256) but the CRB written to by VAS is
+		 * only CRB_SIZE in len.
+		 */
+		fifo = vinst->fault_fifo + (vinst->fault_crbs * CRB_SIZE);
+		entry = fifo;
+
+		if ((entry->stamp.nx.pswid == cpu_to_be32(FIFO_INVALID_ENTRY))
+			|| (entry->ccw & cpu_to_be32(CCW0_INVALID))) {
+			vinst->fifo_in_progress = 0;
+			spin_unlock_irqrestore(&vinst->fault_lock, flags);
+			return IRQ_HANDLED;
+		}
+
+		spin_unlock_irqrestore(&vinst->fault_lock, flags);
+		vinst->fault_crbs++;
+		if (vinst->fault_crbs == (vinst->fault_fifo_size / CRB_SIZE))
+			vinst->fault_crbs = 0;
+
+		memcpy(crb, fifo, CRB_SIZE);
+		entry->stamp.nx.pswid = cpu_to_be32(FIFO_INVALID_ENTRY);
+		entry->ccw |= cpu_to_be32(CCW0_INVALID);
+		/*
+		 * Return credit for the fault window.
+		 */
+		vas_return_credit(vinst->fault_win, false);
+
+		pr_devel("VAS[%d] fault_fifo %p, fifo %p, fault_crbs %d\n",
+				vinst->vas_id, vinst->fault_fifo, fifo,
+				vinst->fault_crbs);
+
+		dump_crb(crb);
+		window = vas_pswid_to_window(vinst,
+				be32_to_cpu(crb->stamp.nx.pswid));
+
+		if (IS_ERR(window)) {
+			/*
+			 * We got an interrupt about a specific send
+			 * window but we can't find that window and we can't
+			 * even clean it up (return credit on user space
+			 * window).
+			 * But we should not get here.
+			 * TODO: Disable IRQ.
+			 */
+			dump_fifo(vinst, (void *)entry);
+			pr_err("VAS[%d] fault_fifo %p, fifo %p, pswid 0x%x, fault_crbs %d bad CRB?\n",
+				vinst->vas_id, vinst->fault_fifo, fifo,
+				be32_to_cpu(crb->stamp.nx.pswid),
+				vinst->fault_crbs);
+
+			WARN_ON_ONCE(1);
+		} else {
+			update_csb(window, crb);
+			/*
+			 * Return credit for send window after processing
+			 * fault CRB.
+			 */
+			vas_return_credit(window, true);
+		}
+	}
+}
+
+irqreturn_t vas_fault_handler(int irq, void *dev_id)
+{
+	struct vas_instance *vinst = dev_id;
+	irqreturn_t ret = IRQ_WAKE_THREAD;
+	unsigned long flags;
+
+	/*
+	 * NX can generate an interrupt for multiple faults. So the
+	 * fault handler thread process all CRBs until finds invalid
+	 * entry. In case if NX sees continuous faults, it is possible
+	 * that the thread function entered with the first interrupt
+	 * can execute and process all valid CRBs.
+	 * So wake up thread only if the fault thread is not in progress.
+	 */
+	spin_lock_irqsave(&vinst->fault_lock, flags);
+
+	if (vinst->fifo_in_progress)
+		ret = IRQ_HANDLED;
+	else
+		vinst->fifo_in_progress = 1;
+
+	spin_unlock_irqrestore(&vinst->fault_lock, flags);
+
+	return ret;
+}
+
+/*
+ * Fault window is opened per VAS instance. NX pastes fault CRB in fault
+ * FIFO upon page faults.
+ */
+int vas_setup_fault_window(struct vas_instance *vinst)
+{
+	struct vas_rx_win_attr attr;
+
+	vinst->fault_fifo_size = VAS_FAULT_WIN_FIFO_SIZE;
+	vinst->fault_fifo = kzalloc(vinst->fault_fifo_size, GFP_KERNEL);
+	if (!vinst->fault_fifo) {
+		pr_err("Unable to alloc %d bytes for fault_fifo\n",
+				vinst->fault_fifo_size);
+		return -ENOMEM;
+	}
+
+	/*
+	 * Invalidate all CRB entries. NX pastes valid entry for each fault.
+	 */
+	memset(vinst->fault_fifo, FIFO_INVALID_ENTRY, vinst->fault_fifo_size);
+	vas_init_rx_win_attr(&attr, VAS_COP_TYPE_FAULT);
+
+	attr.rx_fifo_size = vinst->fault_fifo_size;
+	attr.rx_fifo = __pa(vinst->fault_fifo);
+
+	/*
+	 * Max creds is based on number of CRBs can fit in the FIFO.
+	 * (fault_fifo_size/CRB_SIZE). If 8MB FIFO is used, max creds
+	 * will be 0xffff since the receive creds field is 16bits wide.
+	 */
+	attr.wcreds_max = vinst->fault_fifo_size / CRB_SIZE;
+	attr.lnotify_lpid = 0;
+	attr.lnotify_pid = mfspr(SPRN_PID);
+	attr.lnotify_tid = mfspr(SPRN_PID);
+
+	vinst->fault_win = vas_rx_win_open(vinst->vas_id, VAS_COP_TYPE_FAULT,
+					&attr);
+
+	if (IS_ERR(vinst->fault_win)) {
+		pr_err("VAS: Error %ld opening FaultWin\n",
+			PTR_ERR(vinst->fault_win));
+		kfree(vinst->fault_fifo);
+		return PTR_ERR(vinst->fault_win);
+	}
+
+	pr_devel("VAS: Created FaultWin %d, LPID/PID/TID [%d/%d/%d]\n",
+			vinst->fault_win->winid, attr.lnotify_lpid,
+			attr.lnotify_pid, attr.lnotify_tid);
+
+	return 0;
+}