From: Prasad Pandit Date: Mon, 12 May 2025 12:51:22 +0000 (+0530) Subject: migration: write zero pages when postcopy enabled X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=249543d0c02d7645b8bcda552dad138769e96831;p=thirdparty%2Fqemu.git migration: write zero pages when postcopy enabled During multifd migration, zero pages are written if they are migrated more than once. This may result in a migration thread hang issue when multifd and postcopy are enabled together. When postcopy is enabled, always write zero pages as and when they are migrated. Signed-off-by: Prasad Pandit Reviewed-by: Fabiano Rosas Link: https://lore.kernel.org/r/20250512125124.147064-2-ppandit@redhat.com Signed-off-by: Peter Xu --- diff --git a/migration/multifd-zero-page.c b/migration/multifd-zero-page.c index dbc1184921..4cde868159 100644 --- a/migration/multifd-zero-page.c +++ b/migration/multifd-zero-page.c @@ -85,9 +85,27 @@ void multifd_recv_zero_page_process(MultiFDRecvParams *p) { for (int i = 0; i < p->zero_num; i++) { void *page = p->host + p->zero[i]; - if (ramblock_recv_bitmap_test_byte_offset(p->block, p->zero[i])) { + bool received = + ramblock_recv_bitmap_test_byte_offset(p->block, p->zero[i]); + + /* + * During multifd migration zero page is written to the memory + * only if it is migrated more than once. + * + * It becomes a problem when both multifd & postcopy options are + * enabled. If the zero page which was skipped during multifd phase, + * is accessed during the postcopy phase of the migration, a page + * fault occurs. But this page fault is not served because the + * 'receivedmap' says the zero page is already received. Thus the + * thread accessing that page may hang. + * + * When postcopy is enabled, always write the zero page as and when + * it is migrated. + */ + if (migrate_postcopy_ram() || received) { memset(page, 0, multifd_ram_page_size()); - } else { + } + if (!received) { ramblock_recv_bitmap_set_offset(p->block, p->zero[i]); } }