virtio/console: Add splice_write support

Enable to use splice_write from pipe to virtio-console port.
This steals pages from pipe and directly send it to host.

Note that this may accelerate only the guest to host path.

Changes in v2:
 - Use GFP_KERNEL instead of GFP_ATOMIC in syscall context function.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Acked-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 128 insertions, 8 deletions

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index cdf2f5451c76..730816cdeb45 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -24,6 +24,8 @@
 #include <linux/err.h>
 #include <linux/freezer.h>
 #include <linux/fs.h>
+#include <linux/splice.h>
+#include <linux/pagemap.h>
 #include <linux/init.h>
 #include <linux/list.h>
 #include <linux/poll.h>
@@ -227,6 +229,7 @@ struct port {
         bool guest_connected;
 };
 
+#define MAX_SPLICE_PAGES        32
 /* This is the very early arch-specified put chars function. */
 static int (*early_put_chars)(u32, const char *, int);
 
@@ -474,26 +477,52 @@ static ssize_t send_control_msg(struct port *port, unsigned int event,
         return 0;
 }
 
+struct buffer_token {
+        union {
+                void *buf;
+                struct scatterlist *sg;
+        } u;
+        bool sgpages;
+};
+
+static void reclaim_sg_pages(struct scatterlist *sg)
+{
+        int i;
+        struct page *page;
+
+        for (i = 0; i < MAX_SPLICE_PAGES; i++) {
+                page = sg_page(&sg[i]);
+                if (!page)
+                        break;
+                put_page(page);
+        }
+        kfree(sg);
+}
+
 /* Callers must take the port->outvq_lock */
 static void reclaim_consumed_buffers(struct port *port)
 {
-        void *buf;
+        struct buffer_token *tok;
         unsigned int len;
 
         if (!port->portdev) {
                 /* Device has been unplugged.  vqs are already gone. */
                 return;
         }
-        while ((buf = virtqueue_get_buf(port->out_vq, &len))) {
-                kfree(buf);
+        while ((tok = virtqueue_get_buf(port->out_vq, &len))) {
+                if (tok->sgpages)
+                        reclaim_sg_pages(tok->u.sg);
+                else
+                        kfree(tok->u.buf);
+                kfree(tok);
                 port->outvq_full = false;
         }
 }
 
-static ssize_t send_buf(struct port *port, void *in_buf, size_t in_count,
-                        bool nonblock)
+static ssize_t __send_to_port(struct port *port, struct scatterlist *sg,
+                              int nents, size_t in_count,
+                              struct buffer_token *tok, bool nonblock)
 {
-        struct scatterlist sg[1];
         struct virtqueue *out_vq;
         ssize_t ret;
         unsigned long flags;
@@ -505,8 +534,7 @@ static ssize_t send_buf(struct port *port, void *in_buf, size_t in_count,
 
         reclaim_consumed_buffers(port);
 
-        sg_init_one(sg, in_buf, in_count);
-        ret = virtqueue_add_buf(out_vq, sg, 1, 0, in_buf, GFP_ATOMIC);
+        ret = virtqueue_add_buf(out_vq, sg, nents, 0, tok, GFP_ATOMIC);
 
         /* Tell Host to go! */
         virtqueue_kick(out_vq);
@@ -544,6 +572,37 @@ done:
         return in_count;
 }
 
+static ssize_t send_buf(struct port *port, void *in_buf, size_t in_count,
+                        bool nonblock)
+{
+        struct scatterlist sg[1];
+        struct buffer_token *tok;
+
+        tok = kmalloc(sizeof(*tok), GFP_ATOMIC);
+        if (!tok)
+                return -ENOMEM;
+        tok->sgpages = false;
+        tok->u.buf = in_buf;
+
+        sg_init_one(sg, in_buf, in_count);
+
+        return __send_to_port(port, sg, 1, in_count, tok, nonblock);
+}
+
+static ssize_t send_pages(struct port *port, struct scatterlist *sg, int nents,
+                          size_t in_count, bool nonblock)
+{
+        struct buffer_token *tok;
+
+        tok = kmalloc(sizeof(*tok), GFP_ATOMIC);
+        if (!tok)
+                return -ENOMEM;
+        tok->sgpages = true;
+        tok->u.sg = sg;
+
+        return __send_to_port(port, sg, nents, in_count, tok, nonblock);
+}
+
 /*
  * Give out the data that's requested from the buffer that we have
  * queued up.
@@ -725,6 +784,66 @@ out:
         return ret;
 }
 
+struct sg_list {
+        unsigned int n;
+        size_t len;
+        struct scatterlist *sg;
+};
+
+static int pipe_to_sg(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
+                        struct splice_desc *sd)
+{
+        struct sg_list *sgl = sd->u.data;
+        unsigned int len = 0;
+
+        if (sgl->n == MAX_SPLICE_PAGES)
+                return 0;
+
+        /* Try lock this page */
+        if (buf->ops->steal(pipe, buf) == 0) {
+                /* Get reference and unlock page for moving */
+                get_page(buf->page);
+                unlock_page(buf->page);
+
+                len = min(buf->len, sd->len);
+                sg_set_page(&(sgl->sg[sgl->n]), buf->page, len, buf->offset);
+                sgl->n++;
+                sgl->len += len;
+        }
+
+        return len;
+}
+
+/* Faster zero-copy write by splicing */
+static ssize_t port_fops_splice_write(struct pipe_inode_info *pipe,
+                                      struct file *filp, loff_t *ppos,
+                                      size_t len, unsigned int flags)
+{
+        struct port *port = filp->private_data;
+        struct sg_list sgl;
+        ssize_t ret;
+        struct splice_desc sd = {
+                .total_len = len,
+                .flags = flags,
+                .pos = *ppos,
+                .u.data = &sgl,
+        };
+
+        sgl.n = 0;
+        sgl.len = 0;
+        sgl.sg = kmalloc(sizeof(struct scatterlist) * MAX_SPLICE_PAGES,
+                         GFP_KERNEL);
+        if (unlikely(!sgl.sg))
+                return -ENOMEM;
+
+        sg_init_table(sgl.sg, MAX_SPLICE_PAGES);
+        ret = __splice_from_pipe(pipe, &sd, pipe_to_sg);
+        if (likely(ret > 0))
+                ret = send_pages(port, sgl.sg, sgl.n, sgl.len, true);
+
+        return ret;
+}
+
 static unsigned int port_fops_poll(struct file *filp, poll_table *wait)
 {
         struct port *port;
@@ -856,6 +975,7 @@ static const struct file_operations port_fops = {
         .open  = port_fops_open,
         .read  = port_fops_read,
         .write = port_fops_write,
+        .splice_write = port_fops_splice_write,
         .poll  = port_fops_poll,
         .release = port_fops_release,
         .fasync = port_fops_fasync,