From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41432) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XtyCd-0005En-2x for qemu-devel@nongnu.org; Thu, 27 Nov 2014 07:29:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XtyCW-000495-Td for qemu-devel@nongnu.org; Thu, 27 Nov 2014 07:29:43 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54288) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XtyCW-00048l-L5 for qemu-devel@nongnu.org; Thu, 27 Nov 2014 07:29:36 -0500 From: Stefan Hajnoczi Date: Thu, 27 Nov 2014 12:29:20 +0000 Message-Id: <1417091366-4469-1-git-send-email-stefanha@redhat.com> Subject: [Qemu-devel] [RFC 0/6] memory: make dirty_memory[] accesses atomic List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Peter Maydell , Paolo Bonzini , rth@redhat.com, Stefan Hajnoczi , Juan Quintela The dirty_memory[] bitmap is used for live migration, TCG self-modifying code detection, and VGA emulation. Up until now the bitmap was always accessed under the QEMU global mutex. This series makes all dirty_memory[] accesses atomic to prepare the way for threads writing to guest memory without holding the global mutex. In particular, this series converts non-atomic dirty_memory[] accesses to atomic_or, atomic_xchg, and atomic_fetch_and so that race conditions are avoided when two threads manipulate the bitmap at the same time. There are two pieces remaining before the dirty_memory[] bitmap is truly thread-safe: 1. Convert all cpu_physical_memory_*_dirty() callers to use the API atomically. There are TCG callers who things along the lines of: if (!cpu_physical_memory_get_dirty(addr)) { cpu_physical_memory_set_dirty(addr); /* not atomic! */ } At first I considered ignoring TCG completely since it is currently not multi-threaded, but we might as well tackle this so that virtio-blk/virtio-scsi dataplane can be used with TCG eventually (they still need ioeventfd/irqfd emulation before they can support TCG). 2. Use array RCU to safely resize dirty_memory[] for memory hotplug. Currently ram_block_add() grows the bitmap in a way that is not thread-safe. Paolo has a QEMU userspace RCU implementation which I'd like to bring in for this. I am posting this RFC to get feedback because this is my first foray into the memory bitmap code. Comments appreciated! Stefan Hajnoczi (6): bitmap: add atomic set functions bitmap: add atomic test and clear memory: use atomic ops for setting dirty memory bits migration: move dirty bitmap sync to ram_addr.h memory: replace cpu_physical_memory_reset_dirty() with test-and-clear memory: make cpu_physical_memory_sync_dirty_bitmap() fully atomic arch_init.c | 46 ++---------------------------- cputlb.c | 4 +-- exec.c | 23 +++++++++++---- include/exec/ram_addr.h | 74 ++++++++++++++++++++++++++++++++++++------------- include/qemu/bitmap.h | 4 +++ include/qemu/bitops.h | 14 ++++++++++ memory.c | 11 +++----- util/bitmap.c | 47 +++++++++++++++++++++++++++++++ 8 files changed, 144 insertions(+), 79 deletions(-) -- 2.1.0