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bh=m/f8QL4E3dsHsVYwKyYpzIbZN83Oa7b/hCiQbtuC7g4=; b=PK8D2KS/opTEhH48cJVFy97Bd+ENHQMvdUwV6KRSxWnIKsC5iVhreTvjuync3OBuWExdPh w1e7mMzyrId1umuKzmG0C/2Eva/Tx7aWWyolFrdB+y3xxK01KWN6DNpRdsc2Jrp0f2r7M/ xiQ9P7OPWFsDKEYiWk/du1bhu7ZNTfE= X-MC-Unique: 2HqzFyZhOkWTfC41BTzlRQ-1 From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, leobras@redhat.com, quintela@redhat.com, berrange@redhat.com, peterx@redhat.com, iii@linux.ibm.com, huangy81@chinatelecom.cn Subject: [PULL 09/30] multifd: Copy pages before compressing them with zlib Date: Wed, 20 Jul 2022 12:19:05 +0100 Message-Id: <20220720111926.107055-10-dgilbert@redhat.com> In-Reply-To: <20220720111926.107055-1-dgilbert@redhat.com> References: <20220720111926.107055-1-dgilbert@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 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=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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" X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1658316961810100001 Content-Type: text/plain; charset="utf-8" From: Ilya Leoshkevich zlib_send_prepare() compresses pages of a running VM. zlib does not make any thread-safety guarantees with respect to changing deflate() input concurrently with deflate() [1]. One can observe problems due to this with the IBM zEnterprise Data Compression accelerator capable zlib [2]. When the hardware acceleration is enabled, migration/multifd/tcp/plain/zlib test fails intermittently [3] due to sliding window corruption. The accelerator's architecture explicitly discourages concurrent accesses [4]: Page 26-57, "Other Conditions": As observed by this CPU, other CPUs, and channel programs, references to the parameter block, first, second, and third operands may be multiple-access references, accesses to these storage locations are not necessarily block-concurrent, and the sequence of these accesses or references is undefined. Mark Adler pointed out that vanilla zlib performs double fetches under certain circumstances as well [5], therefore we need to copy data before passing it to deflate(). [1] https://zlib.net/manual.html [2] https://github.com/madler/zlib/pull/410 [3] https://lists.nongnu.org/archive/html/qemu-devel/2022-03/msg03988.html [4] http://publibfp.dhe.ibm.com/epubs/pdf/a227832c.pdf [5] https://lists.gnu.org/archive/html/qemu-devel/2022-07/msg00889.html Signed-off-by: Ilya Leoshkevich Message-Id: <20220705203559.2960949-1-iii@linux.ibm.com> Reviewed-by: Dr. David Alan Gilbert Signed-off-by: Dr. David Alan Gilbert --- migration/multifd-zlib.c | 38 ++++++++++++++++++++++++++++++-------- 1 file changed, 30 insertions(+), 8 deletions(-) diff --git a/migration/multifd-zlib.c b/migration/multifd-zlib.c index 3a7ae44485..18213a9513 100644 --- a/migration/multifd-zlib.c +++ b/migration/multifd-zlib.c @@ -27,6 +27,8 @@ struct zlib_data { uint8_t *zbuff; /* size of compressed buffer */ uint32_t zbuff_len; + /* uncompressed buffer of size qemu_target_page_size() */ + uint8_t *buf; }; =20 /* Multifd zlib compression */ @@ -45,26 +47,38 @@ static int zlib_send_setup(MultiFDSendParams *p, Error = **errp) { struct zlib_data *z =3D g_new0(struct zlib_data, 1); z_stream *zs =3D &z->zs; + const char *err_msg; =20 zs->zalloc =3D Z_NULL; zs->zfree =3D Z_NULL; zs->opaque =3D Z_NULL; if (deflateInit(zs, migrate_multifd_zlib_level()) !=3D Z_OK) { - g_free(z); - error_setg(errp, "multifd %u: deflate init failed", p->id); - return -1; + err_msg =3D "deflate init failed"; + goto err_free_z; } /* This is the maxium size of the compressed buffer */ z->zbuff_len =3D compressBound(MULTIFD_PACKET_SIZE); z->zbuff =3D g_try_malloc(z->zbuff_len); if (!z->zbuff) { - deflateEnd(&z->zs); - g_free(z); - error_setg(errp, "multifd %u: out of memory for zbuff", p->id); - return -1; + err_msg =3D "out of memory for zbuff"; + goto err_deflate_end; + } + z->buf =3D g_try_malloc(qemu_target_page_size()); + if (!z->buf) { + err_msg =3D "out of memory for buf"; + goto err_free_zbuff; } p->data =3D z; return 0; + +err_free_zbuff: + g_free(z->zbuff); +err_deflate_end: + deflateEnd(&z->zs); +err_free_z: + g_free(z); + error_setg(errp, "multifd %u: %s", p->id, err_msg); + return -1; } =20 /** @@ -82,6 +96,8 @@ static void zlib_send_cleanup(MultiFDSendParams *p, Error= **errp) deflateEnd(&z->zs); g_free(z->zbuff); z->zbuff =3D NULL; + g_free(z->buf); + z->buf =3D NULL; g_free(p->data); p->data =3D NULL; } @@ -114,8 +130,14 @@ static int zlib_send_prepare(MultiFDSendParams *p, Err= or **errp) flush =3D Z_SYNC_FLUSH; } =20 + /* + * Since the VM might be running, the page may be changing concurr= ently + * with compression. zlib does not guarantee that this is safe, + * therefore copy the page before calling deflate(). + */ + memcpy(z->buf, p->pages->block->host + p->normal[i], page_size); zs->avail_in =3D page_size; - zs->next_in =3D p->pages->block->host + p->normal[i]; + zs->next_in =3D z->buf; =20 zs->avail_out =3D available; zs->next_out =3D z->zbuff + out_size; --=20 2.36.1