[Qemu-devel] [PATCH v2 0/2] xen: fix gnttab handling with old dom0 kernels

[Qemu-devel] [PATCH v2 0/2] xen: fix gnttab handling with old dom0 kernels

[Juergen Gross]

Trying to start a domain with a qdisk backend on an old dom0 kernel
(non-pvops xen kernel) will fail as xengnttab_set_max_grants() will
succeed only if called directly after opening the gnttab device.

These two patches address the issue by:

- moving the test for availability of xengnttab_grant_copy() from
  the qdisk backend to generic backend handling in order to not have
  to issue the grant copy ioctl with the qdisk specific file handle
- opening the gnttab device in blk_connect() only in order to
  guarantee xengnttab_set_max_grants() is called just after opening
  the gnttab device

Juergen Gross (2):
  xen: add a global indicator for grant copy being available
  xen: dont try setting max grants multiple times

 hw/block/xen_disk.c          | 34 ++++++++++++++++++----------------
 hw/xen/xen_backend.c         | 11 +++++++++++
 include/hw/xen/xen_backend.h |  1 +
 3 files changed, 30 insertions(+), 16 deletions(-)

-- 
2.12.3

[Qemu-devel] [PATCH v2 1/2] xen: add a global indicator for grant copy being available

[Juergen Gross]

The Xen qdisk backend needs to test whether grant copy operations is
available in the kernel. Unfortunately this collides with using
xengnttab_set_max_grants() on some kernels as this operation has to
be the first one after opening the gnttab device.

In order to solve this problem test for the availability of grant copy
in xen_be_init() opening the gnttab device just for that purpose and
closing it again afterwards. Advertise the availability via a global
flag and use that flag in the qdisk backend.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
---
V2:
- gboolean -> bool (Anthony PERARD)
---
 hw/block/xen_disk.c          | 18 ++++++------------
 hw/xen/xen_backend.c         | 11 +++++++++++
 include/hw/xen/xen_backend.h |  1 +
 3 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index 536e2ee735..62506e3167 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -121,9 +121,6 @@ struct XenBlkDev {
     unsigned int        persistent_gnt_count;
     unsigned int        max_grants;
 
-    /* Grant copy */
-    gboolean            feature_grant_copy;
-
     /* qemu block driver */
     DriveInfo           *dinfo;
     BlockBackend        *blk;
@@ -616,7 +613,7 @@ static void qemu_aio_complete(void *opaque, int ret)
         return;
     }
 
-    if (ioreq->blkdev->feature_grant_copy) {
+    if (xen_feature_grant_copy) {
         switch (ioreq->req.operation) {
         case BLKIF_OP_READ:
             /* in case of failure ioreq->aio_errors is increased */
@@ -638,7 +635,7 @@ static void qemu_aio_complete(void *opaque, int ret)
     }
 
     ioreq->status = ioreq->aio_errors ? BLKIF_RSP_ERROR : BLKIF_RSP_OKAY;
-    if (!ioreq->blkdev->feature_grant_copy) {
+    if (!xen_feature_grant_copy) {
         ioreq_unmap(ioreq);
     }
     ioreq_finish(ioreq);
@@ -698,7 +695,7 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
 {
     struct XenBlkDev *blkdev = ioreq->blkdev;
 
-    if (ioreq->blkdev->feature_grant_copy) {
+    if (xen_feature_grant_copy) {
         ioreq_init_copy_buffers(ioreq);
         if (ioreq->req.nr_segments && (ioreq->req.operation == BLKIF_OP_WRITE ||
             ioreq->req.operation == BLKIF_OP_FLUSH_DISKCACHE) &&
@@ -750,7 +747,7 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
     }
     default:
         /* unknown operation (shouldn't happen -- parse catches this) */
-        if (!ioreq->blkdev->feature_grant_copy) {
+        if (!xen_feature_grant_copy) {
             ioreq_unmap(ioreq);
         }
         goto err;
@@ -1010,18 +1007,15 @@ static int blk_init(struct XenDevice *xendev)
 
     blkdev->file_blk  = BLOCK_SIZE;
 
-    blkdev->feature_grant_copy =
-                (xengnttab_grant_copy(blkdev->xendev.gnttabdev, 0, NULL) == 0);
-
     xen_pv_printf(&blkdev->xendev, 3, "grant copy operation %s\n",
-                  blkdev->feature_grant_copy ? "enabled" : "disabled");
+                  xen_feature_grant_copy ? "enabled" : "disabled");
 
     /* fill info
      * blk_connect supplies sector-size and sectors
      */
     xenstore_write_be_int(&blkdev->xendev, "feature-flush-cache", 1);
     xenstore_write_be_int(&blkdev->xendev, "feature-persistent",
-                          !blkdev->feature_grant_copy);
+                          !xen_feature_grant_copy);
     xenstore_write_be_int(&blkdev->xendev, "info", info);
 
     xenstore_write_be_int(&blkdev->xendev, "max-ring-page-order",
diff --git a/hw/xen/xen_backend.c b/hw/xen/xen_backend.c
index c46cbb0759..0f849a26d2 100644
--- a/hw/xen/xen_backend.c
+++ b/hw/xen/xen_backend.c
@@ -44,6 +44,7 @@ BusState *xen_sysbus;
 /* public */
 struct xs_handle *xenstore = NULL;
 const char *xen_protocol;
+bool xen_feature_grant_copy;
 
 /* private */
 static int debug;
@@ -519,6 +520,8 @@ void xenstore_update_fe(char *watch, struct XenDevice *xendev)
 
 int xen_be_init(void)
 {
+    xengnttab_handle *gnttabdev;
+
     xenstore = xs_daemon_open();
     if (!xenstore) {
         xen_pv_printf(NULL, 0, "can't connect to xenstored\n");
@@ -532,6 +535,14 @@ int xen_be_init(void)
         goto err;
     }
 
+    gnttabdev = xengnttab_open(NULL, 0);
+    if (gnttabdev != NULL) {
+        if (xengnttab_grant_copy(gnttabdev, 0, NULL) == 0) {
+            xen_feature_grant_copy = true;
+        }
+        xengnttab_close(gnttabdev);
+    }
+
     xen_sysdev = qdev_create(NULL, TYPE_XENSYSDEV);
     qdev_init_nofail(xen_sysdev);
     xen_sysbus = qbus_create(TYPE_XENSYSBUS, DEVICE(xen_sysdev), "xen-sysbus");
diff --git a/include/hw/xen/xen_backend.h b/include/hw/xen/xen_backend.h
index 8a6fbcbe20..3a27692407 100644
--- a/include/hw/xen/xen_backend.h
+++ b/include/hw/xen/xen_backend.h
@@ -16,6 +16,7 @@
 /* variables */
 extern struct xs_handle *xenstore;
 extern const char *xen_protocol;
+extern bool xen_feature_grant_copy;
 extern DeviceState *xen_sysdev;
 extern BusState *xen_sysbus;
 
-- 
2.12.3

[Qemu-devel] [PATCH v2 2/2] xen: dont try setting max grants multiple times

[Juergen Gross]

Trying to call xengnttab_set_max_grants() with the same file handle
might fail on some kernels, as this operation is allowed only once.

This is a problem for the qdisk backend as blk_connect() can be
called multiple times for a domain, e.g. in case grub-xen is being
used to boot it.

So instead of letting the generic backend code open the gnttab device
do it in blk_connect() and close it again in blk_disconnect.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
V2:
- always call blk_disconnect() from blk_free() in order to have the
  gnttab device node closed (Anthony Perard)
---
 hw/block/xen_disk.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index 62506e3167..e431bd89e8 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -1220,6 +1220,12 @@ static int blk_connect(struct XenDevice *xendev)
     /* Add on the number needed for the ring pages */
     max_grants += blkdev->nr_ring_ref;
 
+    blkdev->xendev.gnttabdev = xengnttab_open(NULL, 0);
+    if (blkdev->xendev.gnttabdev == NULL) {
+        xen_pv_printf(xendev, 0, "xengnttab_open failed: %s\n",
+                      strerror(errno));
+        return -1;
+    }
     if (xengnttab_set_max_grants(blkdev->xendev.gnttabdev, max_grants)) {
         xen_pv_printf(xendev, 0, "xengnttab_set_max_grants failed: %s\n",
                       strerror(errno));
@@ -1327,6 +1333,11 @@ static void blk_disconnect(struct XenDevice *xendev)
         }
         blkdev->feature_persistent = false;
     }
+
+    if (blkdev->xendev.gnttabdev) {
+        xengnttab_close(blkdev->xendev.gnttabdev);
+        blkdev->xendev.gnttabdev = NULL;
+    }
 }
 
 static int blk_free(struct XenDevice *xendev)
@@ -1334,9 +1345,7 @@ static int blk_free(struct XenDevice *xendev)
     struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, xendev);
     struct ioreq *ioreq;
 
-    if (blkdev->blk || blkdev->sring) {
-        blk_disconnect(xendev);
-    }
+    blk_disconnect(xendev);
 
     while (!QLIST_EMPTY(&blkdev->freelist)) {
         ioreq = QLIST_FIRST(&blkdev->freelist);
@@ -1363,7 +1372,6 @@ static void blk_event(struct XenDevice *xendev)
 
 struct XenDevOps xen_blkdev_ops = {
     .size       = sizeof(struct XenBlkDev),
-    .flags      = DEVOPS_FLAG_NEED_GNTDEV,
     .alloc      = blk_alloc,
     .init       = blk_init,
     .initialise    = blk_connect,
-- 
2.12.3

Re: [Qemu-devel] [PATCH v2 2/2] xen: dont try setting max grants multiple times

[Anthony PERARD]

On Fri, Sep 22, 2017 at 02:07:25PM +0200, Juergen Gross wrote:
> Trying to call xengnttab_set_max_grants() with the same file handle
> might fail on some kernels, as this operation is allowed only once.
> 
> This is a problem for the qdisk backend as blk_connect() can be
> called multiple times for a domain, e.g. in case grub-xen is being
> used to boot it.
> 
> So instead of letting the generic backend code open the gnttab device
> do it in blk_connect() and close it again in blk_disconnect.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Acked-by: Anthony PERARD <anthony.perard@citrix.com>

Thanks.

> ---
> V2:
> - always call blk_disconnect() from blk_free() in order to have the
>   gnttab device node closed (Anthony Perard)
> ---
>  hw/block/xen_disk.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
> index 62506e3167..e431bd89e8 100644
> --- a/hw/block/xen_disk.c
> +++ b/hw/block/xen_disk.c
> @@ -1220,6 +1220,12 @@ static int blk_connect(struct XenDevice *xendev)
>      /* Add on the number needed for the ring pages */
>      max_grants += blkdev->nr_ring_ref;
>  
> +    blkdev->xendev.gnttabdev = xengnttab_open(NULL, 0);
> +    if (blkdev->xendev.gnttabdev == NULL) {
> +        xen_pv_printf(xendev, 0, "xengnttab_open failed: %s\n",
> +                      strerror(errno));
> +        return -1;
> +    }
>      if (xengnttab_set_max_grants(blkdev->xendev.gnttabdev, max_grants)) {
>          xen_pv_printf(xendev, 0, "xengnttab_set_max_grants failed: %s\n",
>                        strerror(errno));
> @@ -1327,6 +1333,11 @@ static void blk_disconnect(struct XenDevice *xendev)
>          }
>          blkdev->feature_persistent = false;
>      }
> +
> +    if (blkdev->xendev.gnttabdev) {
> +        xengnttab_close(blkdev->xendev.gnttabdev);
> +        blkdev->xendev.gnttabdev = NULL;
> +    }
>  }
>  
>  static int blk_free(struct XenDevice *xendev)
> @@ -1334,9 +1345,7 @@ static int blk_free(struct XenDevice *xendev)
>      struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, xendev);
>      struct ioreq *ioreq;
>  
> -    if (blkdev->blk || blkdev->sring) {
> -        blk_disconnect(xendev);
> -    }
> +    blk_disconnect(xendev);
>  
>      while (!QLIST_EMPTY(&blkdev->freelist)) {
>          ioreq = QLIST_FIRST(&blkdev->freelist);
> @@ -1363,7 +1372,6 @@ static void blk_event(struct XenDevice *xendev)
>  
>  struct XenDevOps xen_blkdev_ops = {
>      .size       = sizeof(struct XenBlkDev),
> -    .flags      = DEVOPS_FLAG_NEED_GNTDEV,
>      .alloc      = blk_alloc,
>      .init       = blk_init,
>      .initialise    = blk_connect,
> -- 
> 2.12.3
> 

-- 
Anthony PERARD