On 10/23/2012 02:12 PM, Jan Kiszka wrote:
> On 2012-10-22 11:23, Liu Ping Fan wrote:
>> Without biglock, we try to protect the mr by increase refcnt.
>> If we can inc refcnt, go backward and resort to biglock.
>>
>> Another point is memory radix-tree can be flushed by another
>> thread, so we should get the copy of terminal mr to survive
>> from such issue.
>>
>> +
>> void cpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf,
>> int len, int is_write)
>> {
>> @@ -3413,14 +3489,28 @@ void cpu_physical_memory_rw(target_phys_addr_t addr,
>> uint8_t *buf,
>> uint8_t *ptr;
>> uint32_t val;
>> target_phys_addr_t page;
>> - MemoryRegionSection *section;
>> + MemoryRegionSection *section, obj_mrs;
>> + int safe_ref;
>>
>> while (len > 0) {
>> page = addr & TARGET_PAGE_MASK;
>> l = (page + TARGET_PAGE_SIZE) - addr;
>> if (l > len)
>> l = len;
>> - section = phys_page_find(page >> TARGET_PAGE_BITS);
>> + qemu_mutex_lock(&mem_map_lock);
>> + safe_ref = phys_page_lookup(page, &obj_mrs);
>> + qemu_mutex_unlock(&mem_map_lock);
>> + if (safe_ref == 0) {
>> + qemu_mutex_lock_iothread();
>> + qemu_mutex_lock(&mem_map_lock);
>> + /* At the 2nd try, mem map can change, so need to judge it
>> again */
>> + safe_ref = phys_page_lookup(page, &obj_mrs);
>> + qemu_mutex_unlock(&mem_map_lock);
>> + if (safe_ref > 0) {
>> + qemu_mutex_unlock_iothread();
>> + }
>> + }
>> + section = &obj_mrs;
>>
>> if (is_write) {
>> if (!memory_region_is_ram(section->mr)) {
>> @@ -3491,10 +3581,16 @@ void cpu_physical_memory_rw(target_phys_addr_t addr,
>> uint8_t *buf,
>> qemu_put_ram_ptr(ptr);
>> }
>> }
>> +
>> + memory_region_section_unref(&obj_mrs);
>
> The mapping cannot change from not-referenced to reference-counted while
> we were dispatching? I mean the case where we found not ref callback on
> entry and took the big lock, but now there is an unref callback.
We drop the big lock in that case, so we end up in the same situation.
>
>> len -= l;
>> buf += l;
>> addr += l;
>> + if (safe_ref == 0) {
>> + qemu_mutex_unlock_iothread();
>> + }
>> }
>> +
>> }
>>
>> /* used for ROM loading : can write in RAM and ROM */
>> @@ -3504,14 +3600,18 @@ void
>> cpu_physical_memory_write_rom(target_phys_addr_t addr,
>> int l;
>> uint8_t *ptr;
>> target_phys_addr_t page;
>> - MemoryRegionSection *section;
>> + MemoryRegionSection *section, mr_obj;
>>
>> while (len > 0) {
>> page = addr & TARGET_PAGE_MASK;
>> l = (page + TARGET_PAGE_SIZE) - addr;
>> if (l > len)
>> l = len;
>> - section = phys_page_find(page >> TARGET_PAGE_BITS);
>> +
>> + qemu_mutex_lock(&mem_map_lock);
>> + phys_page_lookup(page, &mr_obj);
>> + qemu_mutex_unlock(&mem_map_lock);
>> + section = &mr_obj;
>
> But here we don't care about the return code of phys_page_lookup and all
> related topics? Because we assume the BQL is held? Reminds me that we
> will need some support for assert(qemu_mutex_is_locked(&lock)).
I guess it's better to drop that assumption than to have asymmetric APIs.
>>
>> @@ -4239,9 +4345,12 @@ bool virtio_is_big_endian(void)
>> #ifndef CONFIG_USER_ONLY
>> bool cpu_physical_memory_is_io(target_phys_addr_t phys_addr)
>> {
>> - MemoryRegionSection *section;
>> + MemoryRegionSection *section, mr_obj;
>>
>> - section = phys_page_find(phys_addr >> TARGET_PAGE_BITS);
>> + qemu_mutex_lock(&mem_map_lock);
>> + phys_page_lookup(phys_addr, &mr_obj);
>> + qemu_mutex_unlock(&mem_map_lock);
>> + section = &mr_obj;
>
> Err, no unref needed here?
Need _ref in the name to remind reviewers that it leaves the refcount
unbalanced.
--
error compiling committee.c: too many arguments to function
