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postcopy: Transmit ram size summary word

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Replace the host page-size in the 'advise' command by a pagesize
summary bitmap; if the VM is just using normal RAM then
this will be exactly the same as before, however if they're using
huge pages they'll be different, and thus:
   a) Migration from/to old qemu's that don't understand huge pages
      will fail early.
   b) Migrations with different size RAMBlocks will also fail early.

This catches it very early; earlier than the detailed per-block
check in the next patch.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Message-Id: <20170224182844.32452-2-dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Dr. David Alan Gilbert 2017-02-24 18:28:29 +00:00
parent f9c8caa04f
commit e8ca1db29b
3 changed files with 39 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

32
migration/savevm.c
View file

@ -870,7 +870,7 @@ int qemu_savevm_send_packaged(QEMUFile *f, const uint8_t *buf, size_t len)
void qemu_savevm_send_postcopy_advise(QEMUFile *f)
{
uint64_t tmp[2];
tmp[0] = cpu_to_be64(getpagesize());
tmp[0] = cpu_to_be64(ram_pagesize_summary());
tmp[1] = cpu_to_be64(1ul << qemu_target_page_bits());
trace_qemu_savevm_send_postcopy_advise();
@ -1352,7 +1352,7 @@ static int qemu_loadvm_state_main(QEMUFile *f, MigrationIncomingState *mis);
static int loadvm_postcopy_handle_advise(MigrationIncomingState *mis)
{
PostcopyState ps = postcopy_state_set(POSTCOPY_INCOMING_ADVISE);
uint64_t remote_hps, remote_tps;
uint64_t remote_pagesize_summary, local_pagesize_summary, remote_tps;
trace_loadvm_postcopy_handle_advise();
if (ps != POSTCOPY_INCOMING_NONE) {
@ -1365,17 +1365,27 @@ static int loadvm_postcopy_handle_advise(MigrationIncomingState *mis)
return -1;
}
remote_hps = qemu_get_be64(mis->from_src_file);
if (remote_hps != getpagesize()) {
remote_pagesize_summary = qemu_get_be64(mis->from_src_file);
local_pagesize_summary = ram_pagesize_summary();
if (remote_pagesize_summary != local_pagesize_summary) {
/*
* Some combinations of mismatch are probably possible but it gets
* a bit more complicated. In particular we need to place whole
* host pages on the dest at once, and we need to ensure that we
* handle dirtying to make sure we never end up sending part of
* a hostpage on it's own.
* This detects two potential causes of mismatch:
* a) A mismatch in host page sizes
* Some combinations of mismatch are probably possible but it gets
* a bit more complicated. In particular we need to place whole
* host pages on the dest at once, and we need to ensure that we
* handle dirtying to make sure we never end up sending part of
* a hostpage on it's own.
* b) The use of different huge page sizes on source/destination
* a more fine grain test is performed during RAM block migration
* but this test here causes a nice early clear failure, and
* also fails when passed to an older qemu that doesn't
* do huge pages.
*/
error_report("Postcopy needs matching host page sizes (s=%d d=%d)",
(int)remote_hps, getpagesize());
error_report("Postcopy needs matching RAM page sizes (s=%" PRIx64
" d=%" PRIx64 ")",
remote_pagesize_summary, local_pagesize_summary);
return -1;
}