[PATCH v20210601 37/38] tools: remove migration stream verify code

[Olaf Hering <olaf@xxxxxxxxx>]

The verify code tries to make sure the transferred pages from the paused
domU were received correctly in the previous, final iteration. Every
page is transferred once again by the sender, the receiver compares the
content with what is already mapped into the not-yet started domU.

This does unfortunately not work because a domU has also a number of
pages in its grant table, so that frondend drivers can communicate with
the backend drivers. Since the backend drivers are unaware about the
ongoing saving of the domU, they will continue to write into the shared
pages. As a result the verification of the domU pages will fail.

This is not fixable, so remove the verification code.

The sending side will never send a REC_TYPE_VERIFY record again. It will
silently accept, and ignore the debug flag.

The receiving side will abort an almost complete migration in case it
sees a REC_TYPE_VERIFY record from an old sender. That record is sent at
the very end, it has no way to know in advance that verification was
requested.

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
---
 tools/libs/saverestore/common.h  |  7 ------
 tools/libs/saverestore/restore.c | 43 ++++----------------------------
 tools/libs/saverestore/save.c    | 43 --------------------------------
 3 files changed, 5 insertions(+), 88 deletions(-)

diff --git a/tools/libs/saverestore/common.h b/tools/libs/saverestore/common.h
index b323c1b71a..b8ca24e667 100644
--- a/tools/libs/saverestore/common.h
+++ b/tools/libs/saverestore/common.h
@@ -354,9 +354,6 @@ struct xc_sr_context
             /* Live migrate vs non live suspend. */
             bool live;
 
-            /* Further debugging information in the stream. */
-            bool debug;
-
             unsigned long p2m_size;
             size_t pages_sent;
             size_t overhead_sent;
@@ -418,10 +415,6 @@ struct xc_sr_context
             /* Bitmap of currently populated PFNs during restore. */
             struct xg_sr_bitmap populated_pfns;
 
-            /* Sender has invoked verify mode on the stream. */
-            bool verify;
-            void *verify_buf;
-
             struct xc_sr_restore_arrays *m;
             void *guest_mapping;
             uint32_t nr_mapped_pages;
diff --git a/tools/libs/saverestore/restore.c b/tools/libs/saverestore/restore.c
index d4657e8e57..9a7253a972 100644
--- a/tools/libs/saverestore/restore.c
+++ b/tools/libs/saverestore/restore.c
@@ -337,10 +337,7 @@ static int handle_incoming_page_data(struct xc_sr_context 
*ctx,
             continue;
 
         m->iov[iov_idx].iov_len = PAGE_SIZE;
-        if ( ctx->restore.verify )
-            m->iov[iov_idx].iov_base = ctx->restore.verify_buf + i * PAGE_SIZE;
-        else
-            m->iov[iov_idx].iov_base = m->guest_data[i];
+        m->iov[iov_idx].iov_base = m->guest_data[i];
         iov_idx++;
     }
 
@@ -369,15 +366,6 @@ static int handle_incoming_page_data(struct xc_sr_context 
*ctx,
 
         }
 
-        if ( ctx->restore.verify )
-        {
-            if ( memcmp(m->guest_data[i], m->iov[iov_idx].iov_base, PAGE_SIZE) 
)
-            {
-                ERROR("verify pfn %#"PRIpfn" failed (type %#"PRIx32")",
-                      m->pfns[i], m->types[i] >> XEN_DOMCTL_PFINFO_LTAB_SHIFT);
-            }
-        }
-
         iov_idx++;
     }
 
@@ -447,20 +435,7 @@ static int handle_buffered_page_data(struct xc_sr_context 
*ctx,
 
         }
 
-        if ( ctx->restore.verify )
-        {
-            if ( memcmp(m->guest_data[i], p, PAGE_SIZE) )
-            {
-                errno = EIO;
-                ERROR("verify pfn %#"PRIpfn" failed (type %#"PRIx32")",
-                      m->pfns[i], m->types[i] >> XEN_DOMCTL_PFINFO_LTAB_SHIFT);
-                goto err;
-            }
-        }
-        else
-        {
-            memcpy(m->guest_data[i], p, PAGE_SIZE);
-        }
+        memcpy(m->guest_data[i], p, PAGE_SIZE);
 
         idx++;
     }
@@ -737,17 +712,9 @@ static int process_buffered_record(struct xc_sr_context 
*ctx, struct xc_sr_recor
         break;
 
     case REC_TYPE_VERIFY:
-        DPRINTF("Verify mode enabled");
-        ctx->restore.verify = true;
-        if ( !ctx->restore.verify_buf )
-        {
-            ctx->restore.verify_buf = malloc(MAX_BATCH_SIZE * PAGE_SIZE);
-            if ( !ctx->restore.verify_buf )
-            {
-                rc = -1;
-                PERROR("Unable to allocate verify_buf");
-            }
-        }
+        errno = EINVAL;
+        PERROR("Verify mode is obsolete");
+        rc = -1;
         break;
 
     case REC_TYPE_CHECKPOINT:
diff --git a/tools/libs/saverestore/save.c b/tools/libs/saverestore/save.c
index 523457eaba..2d34822509 100644
--- a/tools/libs/saverestore/save.c
+++ b/tools/libs/saverestore/save.c
@@ -707,41 +707,6 @@ static int suspend_and_send_dirty(struct xc_sr_context 
*ctx)
     return rc;
 }
 
-static int verify_frames(struct xc_sr_context *ctx)
-{
-    xc_interface *xch = ctx->xch;
-    xc_shadow_op_stats_t stats = { 0, ctx->save.p2m_size };
-    int rc;
-    struct xc_sr_record rec = { .type = REC_TYPE_VERIFY };
-
-    DPRINTF("Enabling verify mode");
-
-    rc = write_record(ctx, &rec);
-    if ( rc )
-        goto out;
-
-    xc_set_progress_prefix(xch, "Frames verify");
-    rc = send_all_pages(ctx);
-    if ( rc )
-        goto out;
-
-    if ( xc_shadow_control(
-             xch, ctx->domid, XEN_DOMCTL_SHADOW_OP_PEEK,
-             &ctx->save.dirty_bitmap_hbuf, ctx->save.p2m_size,
-             NULL, 0, &stats) != ctx->save.p2m_size )
-    {
-        PERROR("Failed to retrieve logdirty bitmap");
-        rc = -1;
-        goto out;
-    }
-
-    DPRINTF("  Further stats: faults %u, dirty %u",
-            stats.fault_count, stats.dirty_count);
-
- out:
-    return rc;
-}
-
 /*
  * Send all domain memory.  This is the heart of the live migration loop.
  */
@@ -761,13 +726,6 @@ static int send_domain_memory_live(struct xc_sr_context 
*ctx)
     if ( rc )
         goto out;
 
-    if ( ctx->save.debug )
-    {
-        rc = verify_frames(ctx);
-        if ( rc )
-            goto out;
-    }
-
  out:
     return rc;
 }
@@ -1005,7 +963,6 @@ int xc_domain_save(xc_interface *xch, int io_fd, uint32_t 
dom,
     /* GCC 4.4 (of CentOS 6.x vintage) can' t initialise anonymous unions. */
     ctx.save.callbacks = callbacks;
     ctx.save.live  = !!(flags & XCFLAGS_LIVE);
-    ctx.save.debug = !!(flags & XCFLAGS_DEBUG);
     ctx.save.recv_fd = recv_fd;
 
     if ( xc_domain_getinfo(xch, dom, 1, &ctx.dominfo) != 1 )