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[Qemu-devel] [PULL 32/45] exec: always call qemu_get_ram_ptr within rcu_
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PULL 32/45] exec: always call qemu_get_ram_ptr within rcu_read_lock |
Date: |
Thu, 17 Dec 2015 18:46:28 +0100 |
Simplify the code and document the assumption. The only caller
that is not within rcu_read_lock is memory_region_get_ram_ptr.
Signed-off-by: Paolo Bonzini <address@hidden>
---
exec.c | 22 +++++-----------------
include/exec/memory.h | 9 +++++++--
memory.c | 14 ++++++++++----
3 files changed, 22 insertions(+), 23 deletions(-)
diff --git a/exec.c b/exec.c
index dd11ef9..af95438 100644
--- a/exec.c
+++ b/exec.c
@@ -1786,19 +1786,11 @@ void *qemu_get_ram_block_host_ptr(ram_addr_t addr)
* or address_space_rw instead. For local memory (e.g. video ram) that the
* device owns, use memory_region_get_ram_ptr.
*
- * By the time this function returns, the returned pointer is not protected
- * by RCU anymore. If the caller is not within an RCU critical section and
- * does not hold the iothread lock, it must have other means of protecting the
- * pointer, such as a reference to the region that includes the incoming
- * ram_addr_t.
+ * Called within RCU critical section.
*/
void *qemu_get_ram_ptr(ram_addr_t addr)
{
- RAMBlock *block;
- void *ptr;
-
- rcu_read_lock();
- block = qemu_get_ram_block(addr);
+ RAMBlock *block = qemu_get_ram_block(addr);
if (xen_enabled() && block->host == NULL) {
/* We need to check if the requested address is in the RAM
@@ -1806,17 +1798,12 @@ void *qemu_get_ram_ptr(ram_addr_t addr)
* In that case just map until the end of the page.
*/
if (block->offset == 0) {
- ptr = xen_map_cache(addr, 0, 0);
- goto unlock;
+ return xen_map_cache(addr, 0, 0);
}
block->host = xen_map_cache(block->offset, block->max_length, 1);
}
- ptr = ramblock_ptr(block, addr - block->offset);
-
-unlock:
- rcu_read_unlock();
- return ptr;
+ return ramblock_ptr(block, addr - block->offset);
}
/* Return a host pointer to guest's ram. Similar to qemu_get_ram_ptr
@@ -1954,6 +1941,7 @@ MemoryRegion *qemu_ram_addr_from_host(void *ptr,
ram_addr_t *ram_addr)
return block->mr;
}
+/* Called within RCU critical section. */
static void notdirty_mem_write(void *opaque, hwaddr ram_addr,
uint64_t val, unsigned size)
{
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 0f07159..9bbd247 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -656,8 +656,13 @@ int memory_region_get_fd(MemoryRegion *mr);
* memory_region_get_ram_ptr: Get a pointer into a RAM memory region.
*
* Returns a host pointer to a RAM memory region (created with
- * memory_region_init_ram() or memory_region_init_ram_ptr()). Use with
- * care.
+ * memory_region_init_ram() or memory_region_init_ram_ptr()).
+ *
+ * Use with care; by the time this function returns, the returned pointer is
+ * not protected by RCU anymore. If the caller is not within an RCU critical
+ * section and does not hold the iothread lock, it must have other means of
+ * protecting the pointer, such as a reference to the region that includes
+ * the incoming ram_addr_t.
*
* @mr: the memory region being queried.
*/
diff --git a/memory.c b/memory.c
index 1c1c192..f666c77 100644
--- a/memory.c
+++ b/memory.c
@@ -1577,13 +1577,19 @@ int memory_region_get_fd(MemoryRegion *mr)
void *memory_region_get_ram_ptr(MemoryRegion *mr)
{
- if (mr->alias) {
- return memory_region_get_ram_ptr(mr->alias) + mr->alias_offset;
- }
+ void *ptr;
+ uint64_t offset = 0;
+ rcu_read_lock();
+ while (mr->alias) {
+ offset += mr->alias_offset;
+ mr = mr->alias;
+ }
assert(mr->ram_addr != RAM_ADDR_INVALID);
+ ptr = qemu_get_ram_ptr(mr->ram_addr & TARGET_PAGE_MASK);
+ rcu_read_unlock();
- return qemu_get_ram_ptr(mr->ram_addr & TARGET_PAGE_MASK);
+ return ptr + offset;
}
void memory_region_ram_resize(MemoryRegion *mr, ram_addr_t newsize, Error
**errp)
--
2.5.0
- [Qemu-devel] [PULL 20/45] qemu-char: append opt to stop truncation of serial file, (continued)
- [Qemu-devel] [PULL 20/45] qemu-char: append opt to stop truncation of serial file, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 19/45] kvm: x86: add support for KVM_CAP_SPLIT_IRQCHIP, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 23/45] cris: avoid "naked" qemu_log, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 22/45] alpha: convert "naked" qemu_log to tracepoint, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 24/45] microblaze: avoid "naked" qemu_log, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 21/45] qemu-log: introduce qemu_log_separate, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 27/45] tricore: avoid "naked" qemu_log, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 25/45] s390x: avoid "naked" qemu_log, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 26/45] ppc: cleanup logging, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 29/45] user: introduce "-d page", Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 32/45] exec: always call qemu_get_ram_ptr within rcu_read_lock,
Paolo Bonzini <=
- [Qemu-devel] [PULL 34/45] memory: reorder MemoryRegion fields, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 31/45] linux-user: convert DEBUG_SIGNAL logging to tracepoints, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 30/45] linux-user: avoid "naked" qemu_log, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 28/45] xtensa: avoid "naked" qemu_log, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 35/45] memory: avoid unnecessary object_ref/unref, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 40/45] rcu: optimize rcu_read_lock, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 37/45] memory: extract first iteration of address_space_read and address_space_write, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 41/45] target-i386: kvm: clear unusable segments' flags in migration, Paolo Bonzini, 2015/12/17
- [Qemu-devel] [PULL 43/45] scsi: always call notifier on async cancellation, Paolo Bonzini, 2015/12/17