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Date: Mon, 06 May 2013 13:25:26 +0200
From: Jan Kiszka <jan.kiszka@siemens.com>
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Subject: Re: [Qemu-devel] [PATCH v7 5/7] memory: make mmio dispatch able to
	be out of biglock
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, "gleb@redhat.com" <gleb@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, Marcelo Tosatti <mtosatti@redhat.com>, Liu Ping Fan <qemulist@gmail.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Anthony Liguori <anthony@codemonkey.ws>

On 2013-05-06 13:21, Paolo Bonzini wrote:
> Il 25/11/2012 03:03, Liu Ping Fan ha scritto:
>> @@ -3550,12 +3668,11 @@ void *address_space_map(AddressSpace *as,
>>                          target_phys_addr_t *plen,
>>                          bool is_write)
>>  {
>> -    AddressSpaceDispatch *d = as->dispatch;
>>      target_phys_addr_t len = *plen;
>>      target_phys_addr_t todo = 0;
>>      int l;
>>      target_phys_addr_t page;
>> -    MemoryRegionSection *section;
>> +    MemoryRegionSection *section, mr_obj;
>>      ram_addr_t raddr = RAM_ADDR_MAX;
>>      ram_addr_t rlen;
>>      void *ret;
>> @@ -3565,7 +3682,8 @@ void *address_space_map(AddressSpace *as,
>>          l = (page + TARGET_PAGE_SIZE) - addr;
>>          if (l > len)
>>              l = len;
>> -        section = phys_page_find(d, page >> TARGET_PAGE_BITS);
>> +        address_space_section_lookup_ref(as, page >> TARGET_PAGE_BITS, &mr_obj);
>> +        section = &mr_obj;
>>  
>>          if (!(memory_region_is_ram(section->mr) && !section->readonly)) {
>>              if (todo || bounce.buffer) {
>> @@ -3579,6 +3697,7 @@ void *address_space_map(AddressSpace *as,
>>              }
>>  
>>              *plen = l;
>> +            memory_region_section_unref(&mr_obj);
>>              return bounce.buffer;
>>          }
>>          if (!todo) {
>> @@ -3589,6 +3708,7 @@ void *address_space_map(AddressSpace *as,
>>          len -= l;
>>          addr += l;
>>          todo += l;
>> +        memory_region_section_unref(&mr_obj);
>>      }
>>      rlen = todo;
>>      ret = qemu_ram_ptr_length(raddr, &rlen);
> 
> I think this unref is wrong.  You need to delay it to the
> address_space_unmap, and this in turns requires changing the signature
> of address_space_map.

Can't RAMBlock hold a reference to the associated region? Then this
could be retrieved on unmap without bothering the caller.

Jan

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