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From ccff61f6316a815aa4a538799e089dec7ce754c5 Mon Sep 17 00:00:00 2001
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From: Dr. David Alan Gilbert (git) <dgilbert@redhat.com>
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Date: Thu, 27 Feb 2014 14:53:37 +0100
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Subject: [PATCH 3/6] Fix two XBZRLE corruption issues
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RH-Author: Dr. David Alan Gilbert (git) <dgilbert@redhat.com>
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Message-id: <1393512817-21040-1-git-send-email-dgilbert@redhat.com>
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Patchwork-id: 57921
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O-Subject: [RHEL-7.0 qemu-kvm PATCH 1/1] Fix two XBZRLE corruption issues
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Bugzilla: 1063417
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Juan Quintela <quintela@redhat.com>
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RH-Acked-by: Amit Shah <amit.shah@redhat.com>
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From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
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Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1063417
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Brew: https://brewweb.devel.redhat.com/taskinfo?taskID=7115209
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Upstream: 6d3cb1f970ee85361618f7ff02869180394e012d
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Push zero'd pages into the XBZRLE cache
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    A page that was cached by XBZRLE, zero'd and then XBZRLE'd again
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    was being compared against a stale cache value
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Don't use 'qemu_put_buffer_async' to put pages from the XBZRLE cache
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    Since the cache might change before the data hits the wire
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Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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Signed-off-by: Juan Quintela <quintela@redhat.com>
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(cherry picked from commit 6d3cb1f970ee85361618f7ff02869180394e012d)
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---
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 arch_init.c                    | 64 ++++++++++++++++++++++++++++++++----------
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 include/migration/page_cache.h |  2 +-
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 page_cache.c                   |  2 +-
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 3 files changed, 51 insertions(+), 17 deletions(-)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 arch_init.c                    |   64 ++++++++++++++++++++++++++++++---------
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 include/migration/page_cache.h |    2 +-
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 page_cache.c                   |    2 +-
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 3 files changed, 51 insertions(+), 17 deletions(-)
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diff --git a/arch_init.c b/arch_init.c
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index 31bf690..f5d521a 100644
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--- a/arch_init.c
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+++ b/arch_init.c
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@@ -122,7 +122,6 @@ static void check_guest_throttling(void);
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 #define RAM_SAVE_FLAG_XBZRLE   0x40
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 /* 0x80 is reserved in migration.h start with 0x100 next */
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-
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 static struct defconfig_file {
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     const char *filename;
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     /* Indicates it is an user config file (disabled by -no-user-config) */
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@@ -133,6 +132,7 @@ static struct defconfig_file {
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     { NULL }, /* end of list */
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 };
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+static const uint8_t ZERO_TARGET_PAGE[TARGET_PAGE_SIZE];
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 int qemu_read_default_config_files(bool userconfig)
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 {
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@@ -273,6 +273,34 @@ static size_t save_block_hdr(QEMUFile *f, RAMBlock *block, ram_addr_t offset,
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     return size;
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 }
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+/* This is the last block that we have visited serching for dirty pages
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+ */
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+static RAMBlock *last_seen_block;
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+/* This is the last block from where we have sent data */
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+static RAMBlock *last_sent_block;
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+static ram_addr_t last_offset;
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+static unsigned long *migration_bitmap;
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+static uint64_t migration_dirty_pages;
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+static uint32_t last_version;
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+static bool ram_bulk_stage;
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+
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+/* Update the xbzrle cache to reflect a page that's been sent as all 0.
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+ * The important thing is that a stale (not-yet-0'd) page be replaced
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+ * by the new data.
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+ * As a bonus, if the page wasn't in the cache it gets added so that
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+ * when a small write is made into the 0'd page it gets XBZRLE sent
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+ */
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+static void xbzrle_cache_zero_page(ram_addr_t current_addr)
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+{
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+    if (ram_bulk_stage || !migrate_use_xbzrle()) {
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+        return;
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+    }
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+
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+    /* We don't care if this fails to allocate a new cache page
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+     * as long as it updated an old one */
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+    cache_insert(XBZRLE.cache, current_addr, ZERO_TARGET_PAGE);
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+}
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+
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 #define ENCODING_FLAG_XBZRLE 0x1
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 static int save_xbzrle_page(QEMUFile *f, uint8_t *current_data,
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@@ -329,18 +357,6 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t *current_data,
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     return bytes_sent;
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 }
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-
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-/* This is the last block that we have visited serching for dirty pages
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- */
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-static RAMBlock *last_seen_block;
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-/* This is the last block from where we have sent data */
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-static RAMBlock *last_sent_block;
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-static ram_addr_t last_offset;
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-static unsigned long *migration_bitmap;
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-static uint64_t migration_dirty_pages;
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-static uint32_t last_version;
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-static bool ram_bulk_stage;
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-
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 static inline
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 ram_addr_t migration_bitmap_find_and_reset_dirty(MemoryRegion *mr,
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                                                  ram_addr_t start)
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@@ -512,6 +528,7 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
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         } else {
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             int ret;
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             uint8_t *p;
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+            bool send_async = true;
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             int cont = (block == last_sent_block) ?
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                 RAM_SAVE_FLAG_CONTINUE : 0;
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@@ -522,6 +539,7 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
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             ret = ram_control_save_page(f, block->offset,
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                                offset, TARGET_PAGE_SIZE, &bytes_sent);
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+            current_addr = block->offset + offset;
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             if (ret != RAM_SAVE_CONTROL_NOT_SUPP) {
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                 if (ret != RAM_SAVE_CONTROL_DELAYED) {
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                     if (bytes_sent > 0) {
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@@ -536,19 +554,35 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
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                                             RAM_SAVE_FLAG_COMPRESS);
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                 qemu_put_byte(f, 0);
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                 bytes_sent++;
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+                /* Must let xbzrle know, otherwise a previous (now 0'd) cached
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+                 * page would be stale
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+                 */
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+                xbzrle_cache_zero_page(current_addr);
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             } else if (!ram_bulk_stage && migrate_use_xbzrle()) {
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-                current_addr = block->offset + offset;
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                 bytes_sent = save_xbzrle_page(f, p, current_addr, block,
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                                               offset, cont, last_stage);
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                 if (!last_stage) {
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+                    /* We must send exactly what's in the xbzrle cache
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+                     * even if the page wasn't xbzrle compressed, so that
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+                     * it's right next time.
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+                     */
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                     p = get_cached_data(XBZRLE.cache, current_addr);
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+
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+                    /* Can't send this cached data async, since the cache page
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+                     * might get updated before it gets to the wire
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+                     */
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+                    send_async = false;
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                 }
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             }
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             /* XBZRLE overflow or normal page */
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             if (bytes_sent == -1) {
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                 bytes_sent = save_block_hdr(f, block, offset, cont, RAM_SAVE_FLAG_PAGE);
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-                qemu_put_buffer_async(f, p, TARGET_PAGE_SIZE);
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+                if (send_async) {
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+                    qemu_put_buffer_async(f, p, TARGET_PAGE_SIZE);
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+                } else {
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+                    qemu_put_buffer(f, p, TARGET_PAGE_SIZE);
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+                }
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                 bytes_sent += TARGET_PAGE_SIZE;
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                 acct_info.norm_pages++;
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             }
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diff --git a/include/migration/page_cache.h b/include/migration/page_cache.h
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index d156f0d..2d5ce2d 100644
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--- a/include/migration/page_cache.h
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+++ b/include/migration/page_cache.h
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@@ -66,7 +66,7 @@ uint8_t *get_cached_data(const PageCache *cache, uint64_t addr);
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  * @addr: page address
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  * @pdata: pointer to the page
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  */
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-int cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata);
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+int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata);
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 /**
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  * cache_resize: resize the page cache. In case of size reduction the extra
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diff --git a/page_cache.c b/page_cache.c
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index 250772d..5a763f9 100644
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--- a/page_cache.c
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+++ b/page_cache.c
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@@ -151,7 +151,7 @@ uint8_t *get_cached_data(const PageCache *cache, uint64_t addr)
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     return cache_get_by_addr(cache, addr)->it_data;
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 }
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-int cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata)
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+int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata)
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 {
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     CacheItem *it = NULL;
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-- 
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1.7.1
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