Re: [Qemu-devel] [PATCH for-2.1] exec: fix migration with devices that use address_space_rw

[Michael S. Tsirkin]

On Mon, Jul 21, 2014 at 05:06:44PM +0200, Paolo Bonzini wrote:
> Devices that use address_space_rw to write large areas to memory
> (as opposed to address_space_map/unmap) were broken with respect
> to migration since fe680d0 (exec: Limit translation limiting in
> address_space_translate to xen, 2014-05-07).  Such devices include
> IDE CD-ROMs.
> 
> The reason is that invalidate_and_set_dirty (called by address_space_rw
> but not address_space_map/unmap) was only setting the dirty bit for
> the first page in the translation.
> 
> To fix this, introduce cpu_physical_memory_set_dirty_range_nocode that
> is the same as cpu_physical_memory_set_dirty_range except it does not
> muck with the DIRTY_MEMORY_CODE bitmap.  This function can be used if
> the caller invalidates translations with tb_invalidate_phys_page_range.
> 
> There is another difference between cpu_physical_memory_set_dirty_range
> and cpu_physical_memory_set_dirty_flag; the former includes a call
> to xen_modified_memory.  This is handled separately in
> invalidate_and_set_dirty, and is not needed in other callers of
> cpu_physical_memory_set_dirty_range_nocode, so leave it alone.
> 
> Just one nit: now that invalidate_and_set_dirty takes care of handling
> multiple pages, there is no need for address_space_unmap to wrap it
> in a loop.  In fact that loop would now be O(n^1).
> 
> Reported-by: Dave Gilbert <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>


Reviewed-by: Michael S. Tsirkin <address@hidden>

> ---
>  exec.c                  | 20 ++++----------------
>  include/exec/ram_addr.h | 11 +++++++++++
>  2 files changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 5a2a25e..765bd94 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1568,8 +1568,7 @@ static void notdirty_mem_write(void *opaque, hwaddr 
> ram_addr,
>      default:
>          abort();
>      }
> -    cpu_physical_memory_set_dirty_flag(ram_addr, DIRTY_MEMORY_MIGRATION);
> -    cpu_physical_memory_set_dirty_flag(ram_addr, DIRTY_MEMORY_VGA);
> +    cpu_physical_memory_set_dirty_range_nocode(ram_addr, size);
>      /* we remove the notdirty callback only if the code has been
>         flushed */
>      if (!cpu_physical_memory_is_clean(ram_addr)) {
> @@ -1978,8 +1977,7 @@ static void invalidate_and_set_dirty(hwaddr addr,
>          /* invalidate code */
>          tb_invalidate_phys_page_range(addr, addr + length, 0);
>          /* set dirty bit */
> -        cpu_physical_memory_set_dirty_flag(addr, DIRTY_MEMORY_VGA);
> -        cpu_physical_memory_set_dirty_flag(addr, DIRTY_MEMORY_MIGRATION);
> +        cpu_physical_memory_set_dirty_range_nocode(addr, length);
>      }
>      xen_modified_memory(addr, length);
>  }
> @@ -2335,15 +2333,7 @@ void address_space_unmap(AddressSpace *as, void 
> *buffer, hwaddr len,
>          mr = qemu_ram_addr_from_host(buffer, &addr1);
>          assert(mr != NULL);
>          if (is_write) {
> -            while (access_len) {
> -                unsigned l;
> -                l = TARGET_PAGE_SIZE;
> -                if (l > access_len)
> -                    l = access_len;
> -                invalidate_and_set_dirty(addr1, l);
> -                addr1 += l;
> -                access_len -= l;
> -            }
> +            invalidate_and_set_dirty(addr1, access_len);
>          }
>          if (xen_enabled()) {
>              xen_invalidate_map_cache_entry(buffer);
> @@ -2581,9 +2571,7 @@ void stl_phys_notdirty(AddressSpace *as, hwaddr addr, 
> uint32_t val)
>                  /* invalidate code */
>                  tb_invalidate_phys_page_range(addr1, addr1 + 4, 0);
>                  /* set dirty bit */
> -                cpu_physical_memory_set_dirty_flag(addr1,
> -                                                   DIRTY_MEMORY_MIGRATION);
> -                cpu_physical_memory_set_dirty_flag(addr1, DIRTY_MEMORY_VGA);
> +                cpu_physical_memory_set_dirty_range_nocode(addr1, 4);
>              }
>          }
>      }
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index e9eb831..6593be1 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -71,6 +71,17 @@ static inline void 
> cpu_physical_memory_set_dirty_flag(ram_addr_t addr,
>      set_bit(addr >> TARGET_PAGE_BITS, ram_list.dirty_memory[client]);
>  }
>  
> +static inline void cpu_physical_memory_set_dirty_range_nocode(ram_addr_t 
> start,
> +                                                              ram_addr_t 
> length)
> +{
> +    unsigned long end, page;
> +
> +    end = TARGET_PAGE_ALIGN(start + length) >> TARGET_PAGE_BITS;
> +    page = start >> TARGET_PAGE_BITS;
> +    bitmap_set(ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION], page, end - 
> page);
> +    bitmap_set(ram_list.dirty_memory[DIRTY_MEMORY_VGA], page, end - page);
> +}
> +
>  static inline void cpu_physical_memory_set_dirty_range(ram_addr_t start,
>                                                         ram_addr_t length)
>  {
> -- 
> 1.8.3.1