[Qemu-devel] [PULL 44/57] Postcopy: Use helpers to map pages during migration

[Juan Quintela]

From: "Dr. David Alan Gilbert" 

In postcopy, the destination guest is running at the same time
as it's receiving pages; as we receive new pages we must put
them into the guests address space atomically to avoid a running
CPU accessing a partially written page.

Use the helpers in postcopy-ram.c to map these pages.

qemu_get_buffer_in_place is used to avoid a copy out of qemu_file
in the case that postcopy is going to do a copy anyway.

Signed-off-by: Dr. David Alan Gilbert 
Reviewed-by: Juan Quintela 
Signed-off-by: Juan Quintela 
---
 migration/ram.c | 130 +++-
 trace-events|   1 +
 2 files changed, 130 insertions(+), 1 deletion(-)

diff --git a/migration/ram.c b/migration/ram.c
index d09d5ab..af5f369 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1932,6 +1932,14 @@ static int load_xbzrle(QEMUFile *f, ram_addr_t addr, 
void *host)
 /* Must be called from within a rcu critical section.
  * Returns a pointer from within the RCU-protected ram_list.
  */
+/*
+ * Read a RAMBlock ID from the stream f, find the host address of the
+ * start of that block and add on 'offset'
+ *
+ * f: Stream to read from
+ * offset: Offset within the block
+ * flags: Page flags (mostly to see if it's a continuation of previous block)
+ */
 static inline void *host_from_stream_offset(QEMUFile *f,
 ram_addr_t offset,
 int flags)
@@ -2077,11 +2085,126 @@ int ram_postcopy_incoming_init(MigrationIncomingState 
*mis)
 return postcopy_ram_incoming_init(mis, ram_pages);
 }

+/*
+ * Called in postcopy mode by ram_load().
+ * rcu_read_lock is taken prior to this being called.
+ */
+static int ram_load_postcopy(QEMUFile *f)
+{
+int flags = 0, ret = 0;
+bool place_needed = false;
+bool matching_page_sizes = qemu_host_page_size == TARGET_PAGE_SIZE;
+MigrationIncomingState *mis = migration_incoming_get_current();
+/* Temporary page that is later 'placed' */
+void *postcopy_host_page = postcopy_get_tmp_page(mis);
+
+while (!ret && !(flags & RAM_SAVE_FLAG_EOS)) {
+ram_addr_t addr;
+void *host = NULL;
+void *page_buffer = NULL;
+void *place_source = NULL;
+uint8_t ch;
+bool all_zero = false;
+
+addr = qemu_get_be64(f);
+flags = addr & ~TARGET_PAGE_MASK;
+addr &= TARGET_PAGE_MASK;
+
+trace_ram_load_postcopy_loop((uint64_t)addr, flags);
+place_needed = false;
+if (flags & (RAM_SAVE_FLAG_COMPRESS | RAM_SAVE_FLAG_PAGE)) {
+host = host_from_stream_offset(f, addr, flags);
+if (!host) {
+error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
+ret = -EINVAL;
+break;
+}
+page_buffer = host;
+/*
+ * Postcopy requires that we place whole host pages atomically.
+ * To make it atomic, the data is read into a temporary page
+ * that's moved into place later.
+ * The migration protocol uses,  possibly smaller, target-pages
+ * however the source ensures it always sends all the components
+ * of a host page in order.
+ */
+page_buffer = postcopy_host_page +
+  ((uintptr_t)host & ~qemu_host_page_mask);
+/* If all TP are zero then we can optimise the place */
+if (!((uintptr_t)host & ~qemu_host_page_mask)) {
+all_zero = true;
+}
+
+/*
+ * If it's the last part of a host page then we place the host
+ * page
+ */
+place_needed = (((uintptr_t)host + TARGET_PAGE_SIZE) &
+ ~qemu_host_page_mask) == 0;
+place_source = postcopy_host_page;
+}
+
+switch (flags & ~RAM_SAVE_FLAG_CONTINUE) {
+case RAM_SAVE_FLAG_COMPRESS:
+ch = qemu_get_byte(f);
+memset(page_buffer, ch, TARGET_PAGE_SIZE);
+if (ch) {
+all_zero = false;
+}
+break;
+
+case RAM_SAVE_FLAG_PAGE:
+all_zero = false;
+if (!place_needed || !matching_page_sizes) {
+qemu_get_buffer(f, page_buffer, TARGET_PAGE_SIZE);
+} else {
+/* Avoids the qemu_file copy during postcopy, which is
+ * going to do a copy later; can only do it when we
+ * do this read in one go (matching page sizes)
+ */
+qemu_get_buffer_in_place(f, (uint8_t **)_source,
+ TARGET_PAGE_SIZE);
+}
+break;
+case RAM_SAVE_FLAG_EOS:
+/* normal exit */
+break;
+default:
+

[Qemu-devel] [PULL 44/57] Postcopy: Use helpers to map pages during migration

[Juan Quintela]

From: "Dr. David Alan Gilbert" 

In postcopy, the destination guest is running at the same time
as it's receiving pages; as we receive new pages we must put
them into the guests address space atomically to avoid a running
CPU accessing a partially written page.

Use the helpers in postcopy-ram.c to map these pages.

qemu_get_buffer_in_place is used to avoid a copy out of qemu_file
in the case that postcopy is going to do a copy anyway.

Signed-off-by: Dr. David Alan Gilbert 
Reviewed-by: Juan Quintela 
Signed-off-by: Juan Quintela 
---
 migration/ram.c | 130 +++-
 trace-events|   1 +
 2 files changed, 130 insertions(+), 1 deletion(-)

diff --git a/migration/ram.c b/migration/ram.c
index d09d5ab..af5f369 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1932,6 +1932,14 @@ static int load_xbzrle(QEMUFile *f, ram_addr_t addr, 
void *host)
 /* Must be called from within a rcu critical section.
  * Returns a pointer from within the RCU-protected ram_list.
  */
+/*
+ * Read a RAMBlock ID from the stream f, find the host address of the
+ * start of that block and add on 'offset'
+ *
+ * f: Stream to read from
+ * offset: Offset within the block
+ * flags: Page flags (mostly to see if it's a continuation of previous block)
+ */
 static inline void *host_from_stream_offset(QEMUFile *f,
 ram_addr_t offset,
 int flags)
@@ -2077,11 +2085,126 @@ int ram_postcopy_incoming_init(MigrationIncomingState 
*mis)
 return postcopy_ram_incoming_init(mis, ram_pages);
 }

+/*
+ * Called in postcopy mode by ram_load().
+ * rcu_read_lock is taken prior to this being called.
+ */
+static int ram_load_postcopy(QEMUFile *f)
+{
+int flags = 0, ret = 0;
+bool place_needed = false;
+bool matching_page_sizes = qemu_host_page_size == TARGET_PAGE_SIZE;
+MigrationIncomingState *mis = migration_incoming_get_current();
+/* Temporary page that is later 'placed' */
+void *postcopy_host_page = postcopy_get_tmp_page(mis);
+
+while (!ret && !(flags & RAM_SAVE_FLAG_EOS)) {
+ram_addr_t addr;
+void *host = NULL;
+void *page_buffer = NULL;
+void *place_source = NULL;
+uint8_t ch;
+bool all_zero = false;
+
+addr = qemu_get_be64(f);
+flags = addr & ~TARGET_PAGE_MASK;
+addr &= TARGET_PAGE_MASK;
+
+trace_ram_load_postcopy_loop((uint64_t)addr, flags);
+place_needed = false;
+if (flags & (RAM_SAVE_FLAG_COMPRESS | RAM_SAVE_FLAG_PAGE)) {
+host = host_from_stream_offset(f, addr, flags);
+if (!host) {
+error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
+ret = -EINVAL;
+break;
+}
+page_buffer = host;
+/*
+ * Postcopy requires that we place whole host pages atomically.
+ * To make it atomic, the data is read into a temporary page
+ * that's moved into place later.
+ * The migration protocol uses,  possibly smaller, target-pages
+ * however the source ensures it always sends all the components
+ * of a host page in order.
+ */
+page_buffer = postcopy_host_page +
+  ((uintptr_t)host & ~qemu_host_page_mask);
+/* If all TP are zero then we can optimise the place */
+if (!((uintptr_t)host & ~qemu_host_page_mask)) {
+all_zero = true;
+}
+
+/*
+ * If it's the last part of a host page then we place the host
+ * page
+ */
+place_needed = (((uintptr_t)host + TARGET_PAGE_SIZE) &
+ ~qemu_host_page_mask) == 0;
+place_source = postcopy_host_page;
+}
+
+switch (flags & ~RAM_SAVE_FLAG_CONTINUE) {
+case RAM_SAVE_FLAG_COMPRESS:
+ch = qemu_get_byte(f);
+memset(page_buffer, ch, TARGET_PAGE_SIZE);
+if (ch) {
+all_zero = false;
+}
+break;
+
+case RAM_SAVE_FLAG_PAGE:
+all_zero = false;
+if (!place_needed || !matching_page_sizes) {
+qemu_get_buffer(f, page_buffer, TARGET_PAGE_SIZE);
+} else {
+/* Avoids the qemu_file copy during postcopy, which is
+ * going to do a copy later; can only do it when we
+ * do this read in one go (matching page sizes)
+ */
+qemu_get_buffer_in_place(f, (uint8_t **)_source,
+ TARGET_PAGE_SIZE);
+}
+break;
+case RAM_SAVE_FLAG_EOS:
+/* normal exit */
+break;
+default:
+