* Juan Quintela (quint...@redhat.com) wrote: > <arei.gong...@huawei.com> wrote: > > From: ChenLiang <chenlian...@huawei.com> > > > > Signed-off-by: ChenLiang <chenlian...@huawei.com> > > Signed-off-by: Gonglei <arei.gong...@huawei.com> > > Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com> > > --- > > arch_init.c | 8 +++----- > > 1 file changed, 3 insertions(+), 5 deletions(-) > > > > diff --git a/arch_init.c b/arch_init.c > > index 846e4c5..0d0ba4a 100644 > > --- a/arch_init.c > > +++ b/arch_init.c > > @@ -376,11 +376,8 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t > > **current_data, > > > > prev_cached_page = get_cached_data(XBZRLE.cache, current_addr); > > > > - /* save current buffer into memory */ > > - memcpy(XBZRLE.current_buf, *current_data, TARGET_PAGE_SIZE); > > - > > I think this is wrong. > Remember that now migration is done in parallel with the guest running. > If the guest modifies the page while we are encoding it, we end with a > different contents in the cache and in the real page, and that causes > corruption. > > This way, what we encoded is a "private copy of the page, so we don't > have that problem". > > Makes sense?
Kind of; see back in March I hit this while testing the 1st version of this patch: https://lists.gnu.org/archive/html/qemu-devel/2014-03/msg05631.html but then we had some patches that fixed it; and the discussion was here: https://lists.gnu.org/archive/html/qemu-devel/2014-03/msg05677.html and then I summarized it as: https://lists.gnu.org/archive/html/qemu-devel/2014-03/msg05768.html * It's an interesting, if unusual, observation; it means we can send * completely bogus data at this point because we know it will get * overwritten later; I think the requirements are: * * 1) That we meet the protocol (which seems to require that the run lengths are * not allowed to be 0) * 2) That we don't get stuck in any loops or go over the end of the page * (I think this means we have to be careful of those byte loops within * the word-at-a-time cases) * 3) The page that ends up in our xbzrle cache must match the destination * page, since the next cycle of xbzrle will use it as reference. * Dave > > /* XBZRLE encoding (if there is no overflow) */ > > - encoded_len = xbzrle_encode_buffer(prev_cached_page, > > XBZRLE.current_buf, > > + encoded_len = xbzrle_encode_buffer(prev_cached_page, *current_data, > > TARGET_PAGE_SIZE, > > XBZRLE.encoded_buf, > > TARGET_PAGE_SIZE); > > if (encoded_len == 0) { > > @@ -399,7 +396,8 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t > > **current_data, > > > > /* we need to update the data in the cache, in order to get the same > > data */ > > if (!last_stage) { > > - memcpy(prev_cached_page, XBZRLE.current_buf, TARGET_PAGE_SIZE); > > + xbzrle_decode_buffer(XBZRLE.encoded_buf, encoded_len, > > prev_cached_page, > > + TARGET_PAGE_SIZE); > > } > > > > /* Send XBZRLE based compressed page */ -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK