exec: ram_block_discard_range
Create ram_block_discard_range in exec.c to replace
postcopy_ram_discard_range and most of ram_discard_range.
Those two routines are a bit of a weird combination, and
ram_discard_range is about to get more complex for hugepages.
It's OS dependent code (so shouldn't be in migration/ram.c) but
it needs quite a bit of the innards of RAMBlock so doesn't belong in
the os*.c.
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Message-Id: <20170224182844.32452-5-dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
diff --git a/exec.c b/exec.c
index 3adf2b1..8ac556a 100644
--- a/exec.c
+++ b/exec.c
@@ -45,6 +45,7 @@
#include "exec/address-spaces.h"
#include "sysemu/xen-mapcache.h"
#include "trace-root.h"
+
#endif
#include "exec/cpu-all.h"
#include "qemu/rcu_queue.h"
@@ -3294,4 +3295,57 @@
rcu_read_unlock();
return ret;
}
+
+/*
+ * Unmap pages of memory from start to start+length such that
+ * they a) read as 0, b) Trigger whatever fault mechanism
+ * the OS provides for postcopy.
+ * The pages must be unmapped by the end of the function.
+ * Returns: 0 on success, none-0 on failure
+ *
+ */
+int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length)
+{
+ int ret = -1;
+
+ uint8_t *host_startaddr = rb->host + start;
+
+ if ((uintptr_t)host_startaddr & (rb->page_size - 1)) {
+ error_report("ram_block_discard_range: Unaligned start address: %p",
+ host_startaddr);
+ goto err;
+ }
+
+ if ((start + length) <= rb->used_length) {
+ uint8_t *host_endaddr = host_startaddr + length;
+ if ((uintptr_t)host_endaddr & (rb->page_size - 1)) {
+ error_report("ram_block_discard_range: Unaligned end address: %p",
+ host_endaddr);
+ goto err;
+ }
+
+ errno = ENOTSUP; /* If we are missing MADVISE etc */
+
+#if defined(CONFIG_MADVISE)
+ /* Note: We need the madvise MADV_DONTNEED behaviour of definitely
+ * freeing the page.
+ */
+ ret = madvise(host_startaddr, length, MADV_DONTNEED);
+#endif
+ if (ret) {
+ ret = -errno;
+ error_report("ram_block_discard_range: Failed to discard range "
+ "%s:%" PRIx64 " +%zx (%d)",
+ rb->idstr, start, length, ret);
+ }
+ } else {
+ error_report("ram_block_discard_range: Overrun block '%s' (%" PRIu64
+ "/%zx/" RAM_ADDR_FMT")",
+ rb->idstr, start, length, rb->used_length);
+ }
+
+err:
+ return ret;
+}
+
#endif
