Re: [PATCH v16 QEMU 08/16] vfio: Register SaveVMHandlers for VFIO device

[Yan Zhao]

On Tue, May 05, 2020 at 12:37:26PM +0800, Alex Williamson wrote:
> On Tue, 5 May 2020 04:49:10 +0530
> Kirti Wankhede <address@hidden> wrote:
> 
> > On 3/26/2020 2:32 AM, Alex Williamson wrote:
> > > On Wed, 25 Mar 2020 02:39:06 +0530
> > > Kirti Wankhede <address@hidden> wrote:
> > >   
> > >> Define flags to be used as delimeter in migration file stream.
> > >> Added .save_setup and .save_cleanup functions. Mapped & unmapped 
> > >> migration
> > >> region from these functions at source during saving or pre-copy phase.
> > >> Set VFIO device state depending on VM's state. During live migration, VM 
> > >> is
> > >> running when .save_setup is called, _SAVING | _RUNNING state is set for 
> > >> VFIO
> > >> device. During save-restore, VM is paused, _SAVING state is set for VFIO 
> > >> device.
> > >>
> > >> Signed-off-by: Kirti Wankhede <address@hidden>
> > >> Reviewed-by: Neo Jia <address@hidden>
> > >> ---
> > >>   hw/vfio/migration.c  | 76 
> > >> ++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >>   hw/vfio/trace-events |  2 ++
> > >>   2 files changed, 78 insertions(+)
> > >>
> > >> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> > >> index 22ded9d28cf3..033f76526e49 100644
> > >> --- a/hw/vfio/migration.c
> > >> +++ b/hw/vfio/migration.c
> > >> @@ -8,6 +8,7 @@
> > >>    */
> > >>   
> > >>   #include "qemu/osdep.h"
> > >> +#include "qemu/main-loop.h"
> > >>   #include <linux/vfio.h>
> > >>   
> > >>   #include "sysemu/runstate.h"
> > >> @@ -24,6 +25,17 @@
> > >>   #include "pci.h"
> > >>   #include "trace.h"
> > >>   
> > >> +/*
> > >> + * Flags used as delimiter:
> > >> + * 0xffffffff => MSB 32-bit all 1s
> > >> + * 0xef10     => emulated (virtual) function IO
> > >> + * 0x0000     => 16-bits reserved for flags
> > >> + */
> > >> +#define VFIO_MIG_FLAG_END_OF_STATE      (0xffffffffef100001ULL)
> > >> +#define VFIO_MIG_FLAG_DEV_CONFIG_STATE  (0xffffffffef100002ULL)
> > >> +#define VFIO_MIG_FLAG_DEV_SETUP_STATE   (0xffffffffef100003ULL)
> > >> +#define VFIO_MIG_FLAG_DEV_DATA_STATE    (0xffffffffef100004ULL)
> > >> +
> > >>   static void vfio_migration_region_exit(VFIODevice *vbasedev)
> > >>   {
> > >>       VFIOMigration *migration = vbasedev->migration;
> > >> @@ -126,6 +138,69 @@ static int vfio_migration_set_state(VFIODevice 
> > >> *vbasedev, uint32_t mask,
> > >>       return 0;
> > >>   }
> > >>   
> > >> +/* 
> > >> ---------------------------------------------------------------------- */
> > >> +
> > >> +static int vfio_save_setup(QEMUFile *f, void *opaque)
> > >> +{
> > >> +    VFIODevice *vbasedev = opaque;
> > >> +    VFIOMigration *migration = vbasedev->migration;
> > >> +    int ret;
> > >> +
> > >> +    qemu_put_be64(f, VFIO_MIG_FLAG_DEV_SETUP_STATE);
> > >> +
> > >> +    if (migration->region.mmaps) {
> > >> +        qemu_mutex_lock_iothread();
> > >> +        ret = vfio_region_mmap(&migration->region);
> > >> +        qemu_mutex_unlock_iothread();
> > >> +        if (ret) {
> > >> +            error_report("%s: Failed to mmap VFIO migration region %d: 
> > >> %s",
> > >> +                         vbasedev->name, migration->region.index,
> > >> +                         strerror(-ret));
> > >> +            return ret;
> > >> +        }
> > >> +    }
> > >> +
> > >> +    ret = vfio_migration_set_state(vbasedev, ~0, 
> > >> VFIO_DEVICE_STATE_SAVING);
> > >> +    if (ret) {
> > >> +        error_report("%s: Failed to set state SAVING", vbasedev->name);
> > >> +        return ret;
> > >> +    }
> > >> +
> > >> +    /*
> > >> +     * Save migration region size. This is used to verify migration 
> > >> region size
> > >> +     * is greater than or equal to migration region size at destination
> > >> +     */
> > >> +    qemu_put_be64(f, migration->region.size);  
> > > 
> > > Is this requirement supported by the uapi?    
> > 
> > Yes, on UAPI thread we discussed this:
> > 
> >   * For the user application, data is opaque. The user application 
> > should write
> >   * data in the same order as the data is received and the data should be of
> >   * same transaction size at the source.
> > 
> > data should be same transaction size, so migration region size should be 
> > greater than or equal to the size at source when verifying at destination.
> 
> We are that user application for which the data is opaque, therefore we
> should make no assumptions about how the vendor driver makes use of
> their region.  If we get a transaction that exceeds the end of the
> region, I agree, that would be an error.  But we have no business
> predicting that such a transaction might occur if the vendor driver
> indicates it can support the migration.
> 
> > > The vendor driver operates
> > > within the migration region, but it has no requirement to use the full
> > > extent of the region.  Shouldn't we instead insert the version string
> > > from versioning API Yan proposed?  Is this were we might choose to use
> > > an interface via the vfio API rather than sysfs if we had one?
> > >  
> > 
> > VFIO API cannot be used by libvirt or management tool stack. We need 
> > sysfs as Yan proposed to be used by libvirt or management tool stack.
> 
> It's been a long time, but that doesn't seem like what I was asking.
> The sysfs version checking is used to select a target that is likely to
> succeed, but the migration stream is still generated by a user and the
> vendor driver is still ultimately responsible for validating that
> stream.  I would hope that a vendor migration stream therefore starts
> with information similar to that found in the sysfs interface, allowing
> the receiving vendor driver to validate the source device and vendor
> software version, such that we can fail an incoming migration that the
> vendor driver deems incompatible.  Ideally the vendor driver might also
> include consistency and sequence checking throughout the stream to
> prevent a malicious user from exploiting the internal operation of the
> vendor driver.  Thanks,
> 
maybe we can add a rw field migration_version in
struct vfio_device_migration_info besides sysfs interface ?

when reading it in src, it gets the same string as that from sysfs;
when writing it in target, it returns success or not to check
compatibility and fails the migration early in setup phase.

Thanks
Yan.