Commit 49b24afc authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

exec: always call qemu_get_ram_ptr within rcu_read_lock 



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: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent c8ee0a44

exec.c

+5 −17
Original line number Diff line number Diff line
@@ -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)

{

include/exec/memory.h

+7 −2
Original line number Diff line number Diff line
@@ -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.

 */

memory.c

+10 −4
Original line number Diff line number Diff line
@@ -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)