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Re: [Qemu-devel] [PATCH 0/8 RFC] migration: Introduce side channel for R


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 0/8 RFC] migration: Introduce side channel for RAM
Date: Thu, 03 Oct 2013 10:23:33 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130923 Thunderbird/17.0.9

Il 03/10/2013 06:03, Lei Li ha scritto:
>>>
> 
> Hi Paolo,
> 
> When debugging the code, I realized that this problem might still
> exist. In the incoming part, it will qemu_fopen_pipe() in
> unix_accept_incoming_migration first to enable the load_hook
> callback, the check action of this RAM_SAVE_FLAG_HOOK flags would
> lead to 8 bytes taken. Turns out, it will break normal unix 
> migration (without unix-page-flipping), because no matter normal unix
> migration or unix-page-flipping migration, the incoming side has to
> check this 8-byes flags first to decide whether the load_hook is
> called, and normal unix migration did not send this 8-byte flags.

Why is the load_hook callback being called at all without page flipping?
 Without page flipping, the before_iterate and save_page hook will
return immediately (or depending on your code they may never be called),
so the RAM_SAVE_FLAG_HOOK will never be written to the Unix socket.

> I wonder if I didn't understand your suggestion correctly?

Perhaps you want to discuss this tomorrow morning on #qemu?

Paolo



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