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exec: always call qemu_get_ram_ptr within rcu_read_lock

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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 <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2015-12-16 10:30:47 +01:00
parent c8ee0a445a
commit 49b24afcb1
3 changed files with 22 additions and 23 deletions
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22
exec.c
View File

@ -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)
{

9
include/exec/memory.h
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@ -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.
*/

14
memory.c
View File

@ -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)