143 lines
5.0 KiB
Diff
143 lines
5.0 KiB
Diff
From 1d280070748b604c60a7be4d4c3c3a28e3964f37 Mon Sep 17 00:00:00 2001
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From: Thomas Huth <thuth@redhat.com>
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Date: Tue, 2 Aug 2022 10:11:21 +0200
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Subject: [PATCH 31/32] multifd: Copy pages before compressing them with zlib
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RH-Author: Thomas Huth <thuth@redhat.com>
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RH-MergeRequest: 112: Fix postcopy migration on s390x
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RH-Commit: [1/2] fd5a0221e22b4563bd1cb7f8a8b95f0bfe8f5fc9 (thuth/qemu-kvm-cs9)
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RH-Bugzilla: 2099934
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RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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RH-Acked-by: Cornelia Huck <cohuck@redhat.com>
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RH-Acked-by: David Hildenbrand <david@redhat.com>
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RH-Acked-by: Peter Xu <peterx@redhat.com>
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Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2099934
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zlib_send_prepare() compresses pages of a running VM. zlib does not
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make any thread-safety guarantees with respect to changing deflate()
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input concurrently with deflate() [1].
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One can observe problems due to this with the IBM zEnterprise Data
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Compression accelerator capable zlib [2]. When the hardware
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acceleration is enabled, migration/multifd/tcp/plain/zlib test fails
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intermittently [3] due to sliding window corruption. The accelerator's
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architecture explicitly discourages concurrent accesses [4]:
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Page 26-57, "Other Conditions":
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As observed by this CPU, other CPUs, and channel
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programs, references to the parameter block, first,
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second, and third operands may be multiple-access
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references, accesses to these storage locations are
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not necessarily block-concurrent, and the sequence
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of these accesses or references is undefined.
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Mark Adler pointed out that vanilla zlib performs double fetches under
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certain circumstances as well [5], therefore we need to copy data
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before passing it to deflate().
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[1] https://zlib.net/manual.html
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[2] https://github.com/madler/zlib/pull/410
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[3] https://lists.nongnu.org/archive/html/qemu-devel/2022-03/msg03988.html
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[4] http://publibfp.dhe.ibm.com/epubs/pdf/a227832c.pdf
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[5] https://lists.gnu.org/archive/html/qemu-devel/2022-07/msg00889.html
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Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
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Message-Id: <20220705203559.2960949-1-iii@linux.ibm.com>
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Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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(cherry picked from commit 007e179ef0e97eafda4c9ff2a9d665a1947c7c6d)
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Signed-off-by: Thomas Huth <thuth@redhat.com>
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---
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migration/multifd-zlib.c | 38 ++++++++++++++++++++++++++++++--------
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1 file changed, 30 insertions(+), 8 deletions(-)
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diff --git a/migration/multifd-zlib.c b/migration/multifd-zlib.c
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index 3a7ae44485..18213a9513 100644
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--- a/migration/multifd-zlib.c
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+++ b/migration/multifd-zlib.c
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@@ -27,6 +27,8 @@ struct zlib_data {
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uint8_t *zbuff;
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/* size of compressed buffer */
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uint32_t zbuff_len;
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+ /* uncompressed buffer of size qemu_target_page_size() */
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+ uint8_t *buf;
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};
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/* Multifd zlib compression */
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@@ -45,26 +47,38 @@ static int zlib_send_setup(MultiFDSendParams *p, Error **errp)
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{
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struct zlib_data *z = g_new0(struct zlib_data, 1);
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z_stream *zs = &z->zs;
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+ const char *err_msg;
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zs->zalloc = Z_NULL;
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zs->zfree = Z_NULL;
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zs->opaque = Z_NULL;
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if (deflateInit(zs, migrate_multifd_zlib_level()) != Z_OK) {
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- g_free(z);
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- error_setg(errp, "multifd %u: deflate init failed", p->id);
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- return -1;
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+ err_msg = "deflate init failed";
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+ goto err_free_z;
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}
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/* This is the maxium size of the compressed buffer */
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z->zbuff_len = compressBound(MULTIFD_PACKET_SIZE);
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z->zbuff = g_try_malloc(z->zbuff_len);
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if (!z->zbuff) {
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- deflateEnd(&z->zs);
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- g_free(z);
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- error_setg(errp, "multifd %u: out of memory for zbuff", p->id);
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- return -1;
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+ err_msg = "out of memory for zbuff";
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+ goto err_deflate_end;
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+ }
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+ z->buf = g_try_malloc(qemu_target_page_size());
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+ if (!z->buf) {
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+ err_msg = "out of memory for buf";
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+ goto err_free_zbuff;
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}
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p->data = z;
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return 0;
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+
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+err_free_zbuff:
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+ g_free(z->zbuff);
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+err_deflate_end:
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+ deflateEnd(&z->zs);
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+err_free_z:
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+ g_free(z);
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+ error_setg(errp, "multifd %u: %s", p->id, err_msg);
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+ return -1;
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}
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/**
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@@ -82,6 +96,8 @@ static void zlib_send_cleanup(MultiFDSendParams *p, Error **errp)
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deflateEnd(&z->zs);
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g_free(z->zbuff);
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z->zbuff = NULL;
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+ g_free(z->buf);
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+ z->buf = NULL;
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g_free(p->data);
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p->data = NULL;
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}
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@@ -114,8 +130,14 @@ static int zlib_send_prepare(MultiFDSendParams *p, Error **errp)
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flush = Z_SYNC_FLUSH;
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}
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+ /*
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+ * Since the VM might be running, the page may be changing concurrently
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+ * with compression. zlib does not guarantee that this is safe,
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+ * therefore copy the page before calling deflate().
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+ */
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+ memcpy(z->buf, p->pages->block->host + p->normal[i], page_size);
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zs->avail_in = page_size;
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- zs->next_in = p->pages->block->host + p->normal[i];
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+ zs->next_in = z->buf;
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zs->avail_out = available;
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zs->next_out = z->zbuff + out_size;
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--
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2.31.1
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