[Qemu-devel] [PATCH v2] qxl: add migration blocker to avoid pre-save assert

[Qemu-devel] [PATCH v2] qxl: add migration blocker to avoid pre-save assert

[Gerd Hoffmann]

Cc: 1635339@bugs.launchpad.net
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 hw/display/qxl.h |  1 +
 hw/display/qxl.c | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/hw/display/qxl.h b/hw/display/qxl.h
index d2d49dd..77e5a36 100644
--- a/hw/display/qxl.h
+++ b/hw/display/qxl.h
@@ -40,6 +40,7 @@ typedef struct PCIQXLDevice {
     uint32_t           cmdlog;
 
     uint32_t           guest_bug;
+    Error              *migration_blocker;
 
     enum qxl_mode      mode;
     uint32_t           cmdflags;
diff --git a/hw/display/qxl.c b/hw/display/qxl.c
index c31b293..c1f830c 100644
--- a/hw/display/qxl.c
+++ b/hw/display/qxl.c
@@ -26,6 +26,7 @@
 #include "qemu/queue.h"
 #include "qemu/atomic.h"
 #include "sysemu/sysemu.h"
+#include "migration/migration.h"
 #include "trace.h"
 
 #include "qxl.h"
@@ -639,6 +640,27 @@ static int interface_get_command(QXLInstance *sin, struct QXLCommandExt *ext)
         qxl->guest_primary.commands++;
         qxl_track_command(qxl, ext);
         qxl_log_command(qxl, "cmd", ext);
+        {
+            /*
+             * Windows 8 drivers place qxl commands in the vram
+             * (instead of the ram) bar.  We can't live migrate such a
+             * guest, so add a migration blocker in case we detect
+             * this, to avoid triggering the assert in pre_save().
+             *
+             * https://cgit.freedesktop.org/spice/win32/qxl-wddm-dod/commit/?id=f6e099db39e7d0787f294d5fd0dce328b5210faa
+             */
+            void *msg = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id);
+            if (msg != NULL && (
+                    msg < (void *)qxl->vga.vram_ptr ||
+                    msg > ((void *)qxl->vga.vram_ptr + qxl->vga.vram_size))) {
+                if (!qxl->migration_blocker) {
+                    Error *local_err = NULL;
+                    error_setg(&qxl->migration_blocker,
+                               "qxl: guest bug: command not in ram bar");
+                    migrate_add_blocker(qxl->migration_blocker, &local_err);
+                }
+            }
+        }
         trace_qxl_ring_command_get(qxl->id, qxl_mode_to_string(qxl->mode));
         return true;
     default:
@@ -1236,6 +1258,12 @@ static void qxl_hard_reset(PCIQXLDevice *d, int loadvm)
     qemu_spice_create_host_memslot(&d->ssd);
     qxl_soft_reset(d);
 
+    if (d->migration_blocker) {
+        migrate_del_blocker(d->migration_blocker);
+        error_free(d->migration_blocker);
+        d->migration_blocker = NULL;
+    }
+
     if (startstop) {
         qemu_spice_display_start();
     }
-- 
2.9.3

Re: [Qemu-devel] [PATCH v2] qxl: add migration blocker to avoid pre-save assert

[Marc-André Lureau]

Hi

On Mon, Apr 10, 2017 at 12:27 PM Gerd Hoffmann <kraxel@redhat.com> wrote:

> Cc: 1635339@bugs.launchpad.net
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>
---
>  hw/display/qxl.h |  1 +
>  hw/display/qxl.c | 28 ++++++++++++++++++++++++++++
>  2 files changed, 29 insertions(+)
>
> diff --git a/hw/display/qxl.h b/hw/display/qxl.h
> index d2d49dd..77e5a36 100644
> --- a/hw/display/qxl.h
> +++ b/hw/display/qxl.h
> @@ -40,6 +40,7 @@ typedef struct PCIQXLDevice {
>      uint32_t           cmdlog;
>
>      uint32_t           guest_bug;
> +    Error              *migration_blocker;
>
>      enum qxl_mode      mode;
>      uint32_t           cmdflags;
> diff --git a/hw/display/qxl.c b/hw/display/qxl.c
> index c31b293..c1f830c 100644
> --- a/hw/display/qxl.c
> +++ b/hw/display/qxl.c
> @@ -26,6 +26,7 @@
>  #include "qemu/queue.h"
>  #include "qemu/atomic.h"
>  #include "sysemu/sysemu.h"
> +#include "migration/migration.h"
>  #include "trace.h"
>
>  #include "qxl.h"
> @@ -639,6 +640,27 @@ static int interface_get_command(QXLInstance *sin,
> struct QXLCommandExt *ext)
>          qxl->guest_primary.commands++;
>          qxl_track_command(qxl, ext);
>          qxl_log_command(qxl, "cmd", ext);
> +        {
> +            /*
> +             * Windows 8 drivers place qxl commands in the vram
> +             * (instead of the ram) bar.  We can't live migrate such a
> +             * guest, so add a migration blocker in case we detect
> +             * this, to avoid triggering the assert in pre_save().
> +             *
> +             *
> https://cgit.freedesktop.org/spice/win32/qxl-wddm-dod/commit/?id=f6e099db39e7d0787f294d5fd0dce328b5210faa
> +             */
> +            void *msg = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id);
> +            if (msg != NULL && (
> +                    msg < (void *)qxl->vga.vram_ptr ||
> +                    msg > ((void *)qxl->vga.vram_ptr +
> qxl->vga.vram_size))) {
> +                if (!qxl->migration_blocker) {
> +                    Error *local_err = NULL;
> +                    error_setg(&qxl->migration_blocker,
> +                               "qxl: guest bug: command not in ram bar");
> +                    migrate_add_blocker(qxl->migration_blocker,
> &local_err);
>

What do you do with the local_err? error_report_err() perhaps ?


> +                }
> +            }
> +        }
>          trace_qxl_ring_command_get(qxl->id,
> qxl_mode_to_string(qxl->mode));
>          return true;
>      default:
> @@ -1236,6 +1258,12 @@ static void qxl_hard_reset(PCIQXLDevice *d, int
> loadvm)
>      qemu_spice_create_host_memslot(&d->ssd);
>      qxl_soft_reset(d);
>
> +    if (d->migration_blocker) {
> +        migrate_del_blocker(d->migration_blocker);
> +        error_free(d->migration_blocker);
> +        d->migration_blocker = NULL;
> +    }
> +
>      if (startstop) {
>          qemu_spice_display_start();
>      }
> --
> 2.9.3
>
> --
Marc-André Lureau

Re: [Qemu-devel] [PATCH v2] qxl: add migration blocker to avoid pre-save assert

[Gerd Hoffmann]

  Hi,

> > +                if (!qxl->migration_blocker) {
> > +                    Error *local_err = NULL;
> > +                    error_setg(&qxl->migration_blocker,
> > +                               "qxl: guest bug: command not in ram bar");
> > +                    migrate_add_blocker(qxl->migration_blocker,
> > &local_err);
> >
> 
> What do you do with the local_err? error_report_err() perhaps ?

We can't error out at that point, unlike most migration blockers this
isn't added at device initialization time.

So, yes, we could error_report it, but the message would end up in the
logfile unnoticed, so I'm not sure how useful that is ...

cheers,
  Gerd

Re: [Qemu-devel] [PATCH v2] qxl: add migration blocker to avoid pre-save assert

[Marc-André Lureau]

Hi

On Mon, Apr 10, 2017 at 12:51 PM Gerd Hoffmann <kraxel@redhat.com> wrote:

>   Hi,
>
> > > +                if (!qxl->migration_blocker) {
> > > +                    Error *local_err = NULL;
> > > +                    error_setg(&qxl->migration_blocker,
> > > +                               "qxl: guest bug: command not in ram
> bar");
> > > +                    migrate_add_blocker(qxl->migration_blocker,
> > > &local_err);
> > >
> >
> > What do you do with the local_err? error_report_err() perhaps ?
>
> We can't error out at that point, unlike most migration blockers this
> isn't added at device initialization time.
>
> So, yes, we could error_report it, but the message would end up in the
> logfile unnoticed, so I'm not sure how useful that is ...
>

Well, it may eventually be read if something breaks. Otherwise, you may
just pass a NULL pointer, no?

thanks
-- 
Marc-André Lureau