[Qemu-devel] [PATCH 0/2] migration/postcopy: Disable shared RAM

[Qemu-devel] [PATCH 0/2] migration/postcopy: Disable shared RAM

[Dr. David Alan Gilbert (git)]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Disable postcopy migration when there's shared RAM, we're
still figuring out the details.  Without this patch
there's a chance it might appear to succeed in some
cases.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Dr. David Alan Gilbert (2):
  RAMBlocks: qemu_ram_is_shared
  postcopy: Check for shared memory

 exec.c                    |  5 +++++
 include/exec/cpu-common.h |  1 +
 migration/postcopy-ram.c  | 18 ++++++++++++++++++
 3 files changed, 24 insertions(+)

-- 
2.9.3

[Qemu-devel] [PATCH 1/2] RAMBlocks: qemu_ram_is_shared

[Dr. David Alan Gilbert (git)]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Provide a helper to say whether a RAMBlock was created as a
shared mapping.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 exec.c                    | 5 +++++
 include/exec/cpu-common.h | 1 +
 2 files changed, 6 insertions(+)

diff --git a/exec.c b/exec.c
index aabb035..c2cc455 100644
--- a/exec.c
+++ b/exec.c
@@ -1560,6 +1560,11 @@ const char *qemu_ram_get_idstr(RAMBlock *rb)
     return rb->idstr;
 }
 
+bool qemu_ram_is_shared(RAMBlock *rb)
+{
+    return rb->flags & RAM_SHARED;
+}
+
 /* Called with iothread lock held.  */
 void qemu_ram_set_idstr(RAMBlock *new_block, const char *name, DeviceState *dev)
 {
diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index b62f0d8..4d45a72 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -69,6 +69,7 @@ RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
 void qemu_ram_set_idstr(RAMBlock *block, const char *name, DeviceState *dev);
 void qemu_ram_unset_idstr(RAMBlock *block);
 const char *qemu_ram_get_idstr(RAMBlock *rb);
+bool qemu_ram_is_shared(RAMBlock *rb);
 size_t qemu_ram_pagesize(RAMBlock *block);
 size_t qemu_ram_pagesize_largest(void);
 
-- 
2.9.3

[Qemu-devel] [PATCH 2/2] postcopy: Check for shared memory

[Dr. David Alan Gilbert (git)]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Postcopy doesn't support migration of RAM shared with another process
yet (we've got a bunch of things to understand).
Check for the case and don't allow postcopy to be enabled.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 migration/postcopy-ram.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index effbeb6..dc80dbb 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -95,6 +95,19 @@ static bool ufd_version_check(int ufd)
     return true;
 }
 
+/* Callback from postcopy_ram_supported_by_host block iterator.
+ */
+static int test_range_shared(const char *block_name, void *host_addr,
+                             ram_addr_t offset, ram_addr_t length, void *opaque)
+{
+    if (qemu_ram_is_shared(qemu_ram_block_by_name(block_name))) {
+        error_report("Postcopy on shared RAM (%s) is not yet supported",
+                     block_name);
+        return 1;
+    }
+    return 0;
+}
+
 /*
  * Note: This has the side effect of munlock'ing all of RAM, that's
  * normally fine since if the postcopy succeeds it gets turned back on at the
@@ -127,6 +140,11 @@ bool postcopy_ram_supported_by_host(void)
         goto out;
     }
 
+    /* We don't support postcopy with shared RAM yet */
+    if (qemu_ram_foreach_block(test_range_shared, NULL)) {
+        goto out;
+    }
+
     /*
      * userfault and mlock don't go together; we'll put it back later if
      * it was enabled.
-- 
2.9.3

Re: [Qemu-devel] [PATCH 1/2] RAMBlocks: qemu_ram_is_shared

[Halil Pasic]

On 03/07/2017 07:36 PM, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Provide a helper to say whether a RAMBlock was created as a
> shared mapping.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  exec.c                    | 5 +++++
>  include/exec/cpu-common.h | 1 +
>  2 files changed, 6 insertions(+)
> 
> diff --git a/exec.c b/exec.c
> index aabb035..c2cc455 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1560,6 +1560,11 @@ const char *qemu_ram_get_idstr(RAMBlock *rb)
>      return rb->idstr;
>  }
> 
> +bool qemu_ram_is_shared(RAMBlock *rb)
> +{
> +    return rb->flags & RAM_SHARED;

Hm, it appears to me RAM_SHARED is defined conditionally, that's within 
#if !defined(CONFIG_USER_ONLY)
#endif

The function however seems to be defined and using RAM_SHARED
unconditionally. Either one or the other seems inappropriate to me.

Regards,
Halil

Re: [Qemu-devel] [PATCH 1/2] RAMBlocks: qemu_ram_is_shared

[Dr. David Alan Gilbert]

* Halil Pasic (pasic@linux.vnet.ibm.com) wrote:
> 
> 
> On 03/07/2017 07:36 PM, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > Provide a helper to say whether a RAMBlock was created as a
> > shared mapping.
> > 
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
> >  exec.c                    | 5 +++++
> >  include/exec/cpu-common.h | 1 +
> >  2 files changed, 6 insertions(+)
> > 
> > diff --git a/exec.c b/exec.c
> > index aabb035..c2cc455 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -1560,6 +1560,11 @@ const char *qemu_ram_get_idstr(RAMBlock *rb)
> >      return rb->idstr;
> >  }
> > 
> > +bool qemu_ram_is_shared(RAMBlock *rb)
> > +{
> > +    return rb->flags & RAM_SHARED;
> 
> Hm, it appears to me RAM_SHARED is defined conditionally, that's within 
> #if !defined(CONFIG_USER_ONLY)
> #endif
> 
> The function however seems to be defined and using RAM_SHARED
> unconditionally. Either one or the other seems inappropriate to me.

Oops! Thanks for spotting that; I'll go and fix that.

Dave

> Regards,
> Halil
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK