[PATCH v3 07/10] powerpc/vas: Add paste address mmap fault handler

[Haren Myneni <haren@linux.ibm.com>]

The user space opens VAS windows and issues NX requests by pasting
CRB on the corresponding paste address mmap. When the system looses
credits due to core removal, the kernel has to close the window in
the hypervisor and make the window inactive by unmapping this paste
address. Also the OS has to handle NX request page faults if the user
space issue NX requests.

This handler remap the new paste address with the same VMA when the
window is active again (due to core add with DLPAR). Otherwise
returns paste failure.

Signed-off-by: Haren Myneni <haren@linux.ibm.com>
---
 arch/powerpc/platforms/book3s/vas-api.c | 60 +++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/arch/powerpc/platforms/book3s/vas-api.c b/arch/powerpc/platforms/book3s/vas-api.c
index 2d06bd1b1935..5ceba75c13eb 100644
--- a/arch/powerpc/platforms/book3s/vas-api.c
+++ b/arch/powerpc/platforms/book3s/vas-api.c
@@ -351,6 +351,65 @@ static int coproc_release(struct inode *inode, struct file *fp)
 	return 0;
 }
 
+/*
+ * This fault handler is invoked when the VAS/NX generates page fault on
+ * the paste address. Happens if the kernel closes window in hypervisor
+ * (on PowerVM) due to lost credit or the paste address is not mapped.
+ */
+static vm_fault_t vas_mmap_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct file *fp = vma->vm_file;
+	struct coproc_instance *cp_inst = fp->private_data;
+	struct vas_window *txwin;
+	u64 paste_addr;
+	int ret;
+
+	/*
+	 * window is not opened. Shouldn't expect this error.
+	 */
+	if (!cp_inst || !cp_inst->txwin) {
+		pr_err("%s(): No send window open?\n", __func__);
+		return VM_FAULT_SIGBUS;
+	}
+
+	txwin = cp_inst->txwin;
+	/*
+	 * Fault is coming due to missing from the original mmap.
+	 * Can happen only when the window is closed due to lost
+	 * credit before mmap() or the user space issued NX request
+	 * without mapping.
+	 */
+	if (txwin->task_ref.vma != vmf->vma) {
+		pr_err("%s(): No previous mapping with paste address\n",
+			__func__);
+		return VM_FAULT_SIGBUS;
+	}
+
+	mutex_lock(&txwin->task_ref.mmap_mutex);
+	/*
+	 * The window may be inactive due to lost credit (Ex: core
+	 * removal with DLPAR). When the window is active again when
+	 * the credit is available, remap with the new paste address.
+	 */
+	if (txwin->status == VAS_WIN_ACTIVE) {
+		paste_addr = cp_inst->coproc->vops->paste_addr(txwin);
+		if (paste_addr) {
+			ret = vmf_insert_pfn(vma, vma->vm_start,
+					(paste_addr >> PAGE_SHIFT));
+			mutex_unlock(&txwin->task_ref.mmap_mutex);
+			return ret;
+		}
+	}
+	mutex_unlock(&txwin->task_ref.mmap_mutex);
+
+	return VM_FAULT_SIGBUS;
+
+}
+static const struct vm_operations_struct vas_vm_ops = {
+	.fault = vas_mmap_fault,
+};
+
 static int coproc_mmap(struct file *fp, struct vm_area_struct *vma)
 {
 	struct coproc_instance *cp_inst = fp->private_data;
@@ -417,6 +476,7 @@ static int coproc_mmap(struct file *fp, struct vm_area_struct *vma)
 			paste_addr, vma->vm_start, rc);
 
 	txwin->task_ref.vma = vma;
+	vma->vm_ops = &vas_vm_ops;
 
 out:
 	mutex_unlock(&txwin->task_ref.mmap_mutex);
-- 
2.27.0