* Yury Kotov (yury-ko...@yandex-team.ru) wrote:
> 10.01.2019, 23:14, "Dr. David Alan Gilbert" <dgilb...@redhat.com>:
> > * Yury Kotov (yury-ko...@yandex-team.ru) wrote:
> >> RAM migration has a RAMBlock validation stage (flag
> >> RAM_SAVE_FLAG_MEM_SIZE).
> >> In this stage QEMU checks further information about RAMBlock:
> >> 1. Presence (by idstr),
> >> 2. Length (trying to resize, when differs),
> >> 3. Optional page size.
> >>
> >> This patch adds a check for RAMBlock's offset. Currently we check it
> >> during
> >> RAM pages loading - every RAM page has an offset in its header. But there
> >> is a
> >> case when we don't send RAM pages (see below).
> >>
> >> The following commits introduce a capability (ignore-external) to skip
> >> some
> >> RAM blocks from migration. In such case the migration stream contains only
> >> meta information about RAM blocks to validate them. So, the only way to
> >> check
> >> block's offset is to send it explicitly.
> >>
> >> Signed-off-by: Yury Kotov <yury-ko...@yandex-team.ru>
> >
> > But why check that offsets match? THey aren't supposed to!
> > Offset's are entirely private to each qemu and they're allowed to be
> > different; the only requirement is that the length and name of each
> > RAMBlock matches, then all the operations we do over the migration
> > stream are relative to the start of the block.
> >
>
> Yes, you are right. It seems that instead I should check block->mr->addr.
I don't think that's guaranteed to be the same either; for example
a video buffer or ROM on a PCI card gets mapped into different parts of
the guests physical address space depending on writes into the PCI
bars. Some RAMBlocks dont even have a mapping associated with them.
If you do want to add something here, please don't increment the version
- unless we're desperate I want to keep the version number the same so
that backwards migration works.
Dave
> >
> > One example where they are validly different is where you hotplug some
> > RAM, so for example:
> >
> > source qemu
> > -M 4G
> > hotplug PCI card
> > hotplug 2G
> >
> > destination qemu
> > -M 4G
> > PCI card declared on the command line
> > extra 2G declared on the command line
> >
> > The offsets are different but we can migrate that case fine.
> >
> > Dave
> >
> >> ---
> >> migration/ram.c | 15 +++++++++++++--
> >> 1 file changed, 13 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/migration/ram.c b/migration/ram.c
> >> index 7e7deec4d8..39629254e1 100644
> >> --- a/migration/ram.c
> >> +++ b/migration/ram.c
> >> @@ -3171,6 +3171,7 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
> >> if (migrate_postcopy_ram() && block->page_size !=
> >> qemu_host_page_size) {
> >> qemu_put_be64(f, block->page_size);
> >> }
> >> + qemu_put_be64(f, block->offset);
> >> }
> >>
> >> rcu_read_unlock();
> >> @@ -4031,7 +4032,7 @@ static int ram_load(QEMUFile *f, void *opaque, int
> >> version_id)
> >>
> >> seq_iter++;
> >>
> >> - if (version_id != 4) {
> >> + if (version_id < 4) {
> >> ret = -EINVAL;
> >> }
> >>
> >> @@ -4132,6 +4133,16 @@ static int ram_load(QEMUFile *f, void *opaque, int
> >> version_id)
> >> ret = -EINVAL;
> >> }
> >> }
> >> + if (version_id >= 5) {
> >> + ram_addr_t offset;
> >> + offset = qemu_get_be64(f);
> >> + if (block->offset != offset) {
> >> + error_report("Mismatched RAM block offset %s "
> >> + "%" PRId64 "!= %" PRId64,
> >> + id, offset, (uint64_t)block->offset);
> >> + ret = -EINVAL;
> >> + }
> >> + }
> >> ram_control_load_hook(f, RAM_CONTROL_BLOCK_REG,
> >> block->idstr);
> >> } else {
> >> @@ -4363,5 +4374,5 @@ static SaveVMHandlers savevm_ram_handlers = {
> >> void ram_mig_init(void)
> >> {
> >> qemu_mutex_init(&XBZRLE.lock);
> >> - register_savevm_live(NULL, "ram", 0, 4, &savevm_ram_handlers,
> >> &ram_state);
> >> + register_savevm_live(NULL, "ram", 0, 5, &savevm_ram_handlers,
> >> &ram_state);
> >> }
> >> --
> >> 2.20.1
> > --
> > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
>
> Regards,
> Yury
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
