From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
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 <dgilb...@redhat.com>
---
migration/ram.c | 128 +++++++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 103 insertions(+), 25 deletions(-)
diff --git a/migration/ram.c b/migration/ram.c
index 487e838..6d9cfb5 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1848,7 +1848,17 @@ 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
+ * mis: MigrationIncomingState
+ * 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,
+ MigrationIncomingState *mis,
ram_addr_t offset,
int flags)
{
@@ -2000,6 +2010,15 @@ static int ram_load(QEMUFile *f, void *opaque, int
version_id)
int flags = 0, ret = 0;
static uint64_t seq_iter;
int len = 0;
+ MigrationIncomingState *mis = migration_incoming_get_current();
+ /*
+ * If system is running in postcopy mode, page inserts to host memory must
+ * be atomic
+ */
+ bool postcopy_running = postcopy_state_get() >=
POSTCOPY_INCOMING_LISTENING;
+ void *postcopy_host_page = NULL;
+ bool postcopy_place_needed = false;
+ bool matching_page_sizes = qemu_host_page_size == TARGET_PAGE_SIZE;
seq_iter++;
@@ -2015,13 +2034,55 @@ static int ram_load(QEMUFile *f, void *opaque, int
version_id)
rcu_read_lock();
while (!ret && !(flags & RAM_SAVE_FLAG_EOS)) {
ram_addr_t addr, total_ram_bytes;
- void *host;
+ void *host = NULL;
+ void *page_buffer = NULL;
+ void *postcopy_place_source = NULL;
uint8_t ch;
+ bool all_zero = false;
addr = qemu_get_be64(f);
flags = addr & ~TARGET_PAGE_MASK;
addr &= TARGET_PAGE_MASK;
+ postcopy_place_needed = false;
+ if (flags & (RAM_SAVE_FLAG_COMPRESS | RAM_SAVE_FLAG_PAGE |
+ RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) {
+ host = host_from_stream_offset(f, mis, addr, flags);
+ if (!host) {
+ error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
+ ret = -EINVAL;
+ break;
+ }
+ page_buffer = host;
+ if (postcopy_running) {
+ /*
+ * 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.
+ */
+ if (!postcopy_host_page) {
+ postcopy_host_page = postcopy_get_tmp_page(mis);
+ }
+ 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
+ */
+ postcopy_place_needed = (((uintptr_t)host + TARGET_PAGE_SIZE) &
+ ~qemu_host_page_mask) == 0;
+ postcopy_place_source = postcopy_host_page;
+ }
+ }
+
switch (flags & ~RAM_SAVE_FLAG_CONTINUE) {
case RAM_SAVE_FLAG_MEM_SIZE:
/* Synchronize RAM block list */
@@ -2062,32 +2123,36 @@ static int ram_load(QEMUFile *f, void *opaque, int
version_id)
}
break;
case RAM_SAVE_FLAG_COMPRESS:
- host = host_from_stream_offset(f, addr, flags);
- if (!host) {
- error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
- ret = -EINVAL;
- break;
- }
ch = qemu_get_byte(f);
- ram_handle_compressed(host, ch, TARGET_PAGE_SIZE);
+ if (!postcopy_running) {
+ ram_handle_compressed(host, ch, TARGET_PAGE_SIZE);
+ } else {
+ memset(page_buffer, ch, TARGET_PAGE_SIZE);
+ if (ch) {
+ all_zero = false;
+ }
+ }
break;
+
case 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;
+ all_zero = false;
+ if (!postcopy_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 **)&postcopy_place_source,
+ TARGET_PAGE_SIZE);
}
- qemu_get_buffer(f, host, TARGET_PAGE_SIZE);
break;
case RAM_SAVE_FLAG_COMPRESS_PAGE:
- host = host_from_stream_offset(f, addr, flags);
- if (!host) {
- error_report("Invalid RAM offset " RAM_ADDR_FMT, addr);
- ret = -EINVAL;
- break;
+ all_zero = false;
+ if (postcopy_running) {
+ error_report("Compressed RAM in postcopy mode @%zx\n", addr);
+ return -EINVAL;
}
-
len = qemu_get_be32(f);
if (len < 0 || len > compressBound(TARGET_PAGE_SIZE)) {
error_report("Invalid compressed data length: %d", len);
@@ -2097,12 +2162,12 @@ static int ram_load(QEMUFile *f, void *opaque, int
version_id)
qemu_get_buffer(f, compressed_data_buf, len);
decompress_data_with_multi_threads(compressed_data_buf, host, len);
break;
+
case RAM_SAVE_FLAG_XBZRLE:
- host = host_from_stream_offset(f, addr, flags);
- if (!host) {
- error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
- ret = -EINVAL;
- break;
+ all_zero = false;
+ if (postcopy_running) {
+ error_report("XBZRLE RAM block in postcopy mode @%zx\n", addr);
+ return -EINVAL;
}
if (load_xbzrle(f, addr, host) < 0) {
error_report("Failed to decompress XBZRLE page at "
@@ -2123,6 +2188,19 @@ static int ram_load(QEMUFile *f, void *opaque, int
version_id)
ret = -EINVAL;
}
}
+
+ if (postcopy_place_needed) {
+ /* This gets called at the last target page in the host page */
+ if (!all_zero) {
+ ret = postcopy_place_page(mis, host + TARGET_PAGE_SIZE -
+ qemu_host_page_size,
+ postcopy_place_source);
+ } else {
+ ret = postcopy_place_page_zero(mis,
+ host + TARGET_PAGE_SIZE -
+ qemu_host_page_size);
+ }
+ }
if (!ret) {
ret = qemu_file_get_error(f);
}
--
2.5.0
