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Mon, 03 Nov 2025 13:06:35 -0800 (PST) X-Google-Smtp-Source: AGHT+IGEBccPJ2ZtzRCk96hACALrtMDOoWpI6fDmTxDKgAOLO9u8FoW2mA5LVsCIE6WvRVk92ZxL6Q== X-Received: by 2002:a05:620a:4410:b0:89a:2d9b:74ea with SMTP id af79cd13be357-8ab9afd428cmr1658504685a.42.1762203994894; Mon, 03 Nov 2025 13:06:34 -0800 (PST) From: Peter Xu To: qemu-devel@nongnu.org Cc: Fabiano Rosas , David Hildenbrand , peterx@redhat.com, Paolo Bonzini , Marco Cavenati Subject: [PULL 05/36] migration: mapped-ram: handle zero pages Date: Mon, 3 Nov 2025 16:05:54 -0500 Message-ID: <20251103210625.3689448-6-peterx@redhat.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20251103210625.3689448-1-peterx@redhat.com> References: <20251103210625.3689448-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1762204195384154100 Content-Type: text/plain; charset="utf-8" From: Marco Cavenati Make mapped-ram compatible with loadvm snapshot restoring by explicitly zeroing memory pages in this case. Skip zeroing for -incoming and -loadvm migrations to preserve performance. Signed-off-by: Marco Cavenati Link: https://lore.kernel.org/r/20251010115954.1995298-3-Marco.Cavenati@eur= ecom.fr Signed-off-by: Peter Xu --- migration/options.c | 1 - migration/ram.c | 59 ++++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 58 insertions(+), 2 deletions(-) diff --git a/migration/options.c b/migration/options.c index d9227809d7..e78324b80c 100644 --- a/migration/options.c +++ b/migration/options.c @@ -449,7 +449,6 @@ INITIALIZE_MIGRATE_CAPS_SET(check_caps_background_snaps= hot, static const INITIALIZE_MIGRATE_CAPS_SET(check_caps_savevm, MIGRATION_CAPABILITY_MULTIFD, - MIGRATION_CAPABILITY_MAPPED_RAM, ); =20 static bool migrate_incoming_started(void) diff --git a/migration/ram.c b/migration/ram.c index 1384748193..29f016cb25 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -4038,12 +4038,58 @@ static size_t ram_load_multifd_pages(void *host_add= r, size_t size, return size; } =20 +/** + * handle_zero_mapped_ram: Zero out a range of RAM pages if required during + * mapped-ram load + * + * Zeroing is only performed when restoring from a snapshot (HMP loadvm). + * During incoming migration or -loadvm cli snapshot load, the function is= a + * no-op and returns true as in those cases the pages are already guarante= ed to + * be zeroed. + * + * Returns: true on success, false on error (with @errp set). + * @from_bit_idx: Starting index relative to the map of the page (inclusiv= e) + * @to_bit_idx: Ending index relative to the map of the page (exclusive) + */ +static bool handle_zero_mapped_ram(RAMBlock *block, unsigned long from_bit= _idx, + unsigned long to_bit_idx, Error **errp) +{ + ERRP_GUARD(); + ram_addr_t offset; + size_t size; + void *host; + + /* + * Zeroing is not needed for either -loadvm (RUN_STATE_PRELAUNCH), or + * -incoming (RUN_STATE_INMIGRATE). + */ + if (!runstate_check(RUN_STATE_RESTORE_VM)) { + return true; + } + + if (from_bit_idx >=3D to_bit_idx) { + return true; + } + + size =3D TARGET_PAGE_SIZE * (to_bit_idx - from_bit_idx); + offset =3D from_bit_idx << TARGET_PAGE_BITS; + host =3D host_from_ram_block_offset(block, offset); + if (!host) { + error_setg(errp, "zero page outside of ramblock %s range", + block->idstr); + return false; + } + ram_handle_zero(host, size); + + return true; +} + static bool read_ramblock_mapped_ram(QEMUFile *f, RAMBlock *block, long num_pages, unsigned long *bitmap, Error **errp) { ERRP_GUARD(); - unsigned long set_bit_idx, clear_bit_idx; + unsigned long set_bit_idx, clear_bit_idx =3D 0; ram_addr_t offset; void *host; size_t read, unread, size; @@ -4052,6 +4098,12 @@ static bool read_ramblock_mapped_ram(QEMUFile *f, RA= MBlock *block, set_bit_idx < num_pages; set_bit_idx =3D find_next_bit(bitmap, num_pages, clear_bit_idx + = 1)) { =20 + /* Zero pages */ + if (!handle_zero_mapped_ram(block, clear_bit_idx, set_bit_idx, err= p)) { + return false; + } + + /* Non-zero pages */ clear_bit_idx =3D find_next_zero_bit(bitmap, num_pages, set_bit_id= x + 1); =20 unread =3D TARGET_PAGE_SIZE * (clear_bit_idx - set_bit_idx); @@ -4083,6 +4135,11 @@ static bool read_ramblock_mapped_ram(QEMUFile *f, RA= MBlock *block, } } =20 + /* Handle trailing 0 pages */ + if (!handle_zero_mapped_ram(block, clear_bit_idx, num_pages, errp)) { + return false; + } + return true; =20 err: --=20 2.50.1