Re: [Qemu-devel] [PATCH v4 32/47] postcopy: ram_enable_notify to switch on userfault

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* David Gibson (david@gibson.dropbear.id.au) wrote:
> On Fri, Oct 03, 2014 at 06:47:38PM +0100, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
> >  include/migration/migration.h    |  2 ++
> >  include/migration/postcopy-ram.h |  6 +++++
> >  postcopy-ram.c                   | 49 +++++++++++++++++++++++++++++++++++++++-
> >  savevm.c                         |  9 ++++++++
> >  4 files changed, 65 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/migration/migration.h b/include/migration/migration.h
> > index be63c89..b01cc17 100644
> > --- a/include/migration/migration.h
> > +++ b/include/migration/migration.h
> > @@ -87,6 +87,8 @@ struct MigrationIncomingState {
> >          POSTCOPY_RAM_INCOMING_END
> >      } postcopy_ram_state;
> >  
> > +    /* For the kernel to send us notifications */
> > +    int            userfault_fd;
> >      QEMUFile *return_path;
> >      QemuMutex      rp_mutex;    /* We send replies from multiple threads */
> >      PostcopyPMI    postcopy_pmi;
> > diff --git a/include/migration/postcopy-ram.h b/include/migration/postcopy-ram.h
> > index 8f237a2..413b670 100644
> > --- a/include/migration/postcopy-ram.h
> > +++ b/include/migration/postcopy-ram.h
> > @@ -19,6 +19,12 @@
> >  int postcopy_ram_hosttest(void);
> >  
> >  /*
> > + * Make all of RAM sensitive to accesses to areas that haven't yet been written
> > + * and wire up anything necessary to deal with it.
> > + */
> > +int postcopy_ram_enable_notify(MigrationIncomingState *mis);
> > +
> > +/*
> >   * Initialise postcopy-ram, setting the RAM to a state where we can go into
> >   * postcopy later; must be called prior to any precopy.
> >   * called from arch_init's similarly named ram_postcopy_incoming_init
> > diff --git a/postcopy-ram.c b/postcopy-ram.c
> > index 8eccf26..925ac77 100644
> > --- a/postcopy-ram.c
> > +++ b/postcopy-ram.c
> > @@ -485,9 +485,51 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
> >      return 0;
> >  }
> >  
> > +/*
> > + * Mark the given area of RAM as requiring notification to unwritten areas
> > + * Used as a  callback on qemu_ram_foreach_block.
> > + *   host_addr: Base of area to mark
> > + *   offset: Offset in the whole ram arena
> > + *   length: Length of the section
> > + *   opaque: Unused
> 
>                 ^^^^^^
> This appears to be wrong - opaque is used to find the MIS.

Fixed.

> 
> > + * Returns 0 on success
> > + */
> > +static int postcopy_ram_sensitise_area(const char *block_name, void *host_addr,
> > +                                       ram_addr_t offset, ram_addr_t length,
> > +                                       void *opaque)
> > +{
> > +    MigrationIncomingState *mis = opaque;
> > +    uint64_t tokern[2];
> 
> "tokern"?

Now "to_kernel"

Dave

> 
> > +
> > +    if (madvise(host_addr, length, MADV_USERFAULT)) {
> > +        perror("postcopy_ram_sensitise_area madvise");
> > +        return -1;
> > +    }
> > +
> > +    /* Now tell our userfault_fd that it's responsible for this area */
> > +    tokern[0] = (uint64_t)(uintptr_t)host_addr | 1; /* 1 means register area */
> > +    tokern[1] = (uint64_t)(uintptr_t)host_addr + length;
> > +    if (write(mis->userfault_fd, tokern, 16) != 16) {
> > +        perror("postcopy_ram_sensitise_area write");
> > +        madvise(host_addr, length, MADV_NOUSERFAULT);
> > +        return -1;
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> > +int postcopy_ram_enable_notify(MigrationIncomingState *mis)
> > +{
> > +    /* Mark so that we get notified of accesses to unwritten areas */
> > +    if (qemu_ram_foreach_block(postcopy_ram_sensitise_area, mis)) {
> > +        return -1;
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> >  #else
> >  /* No target OS support, stubs just fail */
> > -
> >  int postcopy_ram_hosttest(void)
> >  {
> >      error_report("postcopy_ram_hosttest: No OS support");
> > @@ -528,6 +570,11 @@ int postcopy_ram_discard_range(MigrationIncomingState *mis, uint8_t *start,
> >  {
> >      assert(0);
> >  }
> > +
> > +int postcopy_ram_enable_notify(MigrationIncomingState *mis)
> > +{
> > +    assert(0);
> > +}
> >  #endif
> >  
> >  /* ------------------------------------------------------------------------- */
> > diff --git a/savevm.c b/savevm.c
> > index 54bdb26..859c96f 100644
> > --- a/savevm.c
> > +++ b/savevm.c
> > @@ -1304,6 +1304,15 @@ static int loadvm_postcopy_ram_handle_listen(MigrationIncomingState *mis)
> >  
> >      mis->postcopy_ram_state = POSTCOPY_RAM_INCOMING_LISTENING;
> >  
> > +    /*
> > +     * Sensitise RAM - can now generate requests for blocks that don't exist
> > +     * However, at this point the CPU shouldn't be running, and the IO
> > +     * shouldn't be doing anything yet so don't actually expect requests
> > +     */
> > +    if (postcopy_ram_enable_notify(mis)) {
> > +        return -1;
> > +    }
> > +
> >      /* TODO start up the postcopy listening thread */
> >      return 0;
> >  }
> 
> -- 
> David Gibson			| I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
> 				| _way_ _around_!
> http://www.ozlabs.org/~dgibson


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