Re: [Qemu-devel] [PATCH v4] migration: do not rom_reset() during incoming migration

[Peter Xu]

On Mon, Apr 08, 2019 at 04:42:13AM -0400, Catherine Ho wrote:
> Commit 18269069c310 ("migration: Introduce ignore-shared capability")
> addes ignore-shared capability to bypass the shared ramblock (e,g,
> membackend + numa node). It does good to live migration.
> 
> As told by Yury,this commit expectes that QEMU doesn't write to guest RAM
> until VM starts, but it does on aarch64 qemu:
> Backtrace:
> 1  0x000055f4a296dd84 in address_space_write_rom_internal () at
> exec.c:3458
> 2  0x000055f4a296de3a in address_space_write_rom () at exec.c:3479
> 3  0x000055f4a2d519ff in rom_reset () at hw/core/loader.c:1101
> 4  0x000055f4a2d475ec in qemu_devices_reset () at hw/core/reset.c:69
> 5  0x000055f4a2c90a28 in qemu_system_reset () at vl.c:1675
> 6  0x000055f4a2c9851d in main () at vl.c:4552
> 
> Actually, on arm64 virt marchine, ramblock "dtb" will be filled into ram
> druing rom_reset. In ignore-shared incoming case, this rom filling
> is not required since all the data has been stored in memory backend
> file.
> 
> Further more, as suggested by Peter Xu, if we do rom_reset() now with
> these ROMs then the RAM data should be re-filled again too with the
> migration stream coming in.
> 
> Fixes: commit 18269069c310 ("migration: Introduce ignore-shared
> capability")
> Suggested-by: Yury Kotov <address@hidden>
> Suggested-by: Peter Xu <address@hidden>
> Signed-off-by: Catherine Ho <address@hidden>

Acked-by: Peter Xu <address@hidden>

-- 
Peter Xu