Messages in this thread | | | Subject | Re: [PATCH] kexec based hibernation: a prototype of kexec multi-stage load | From | "Huang, Ying" <> | Date | Fri, 16 May 2008 12:52:48 +0800 |
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On Thu, 2008-05-15 at 19:55 -0700, Eric W. Biederman wrote: > "Huang, Ying" <ying.huang@intel.com> writes: > > > The disadvantage of this solution is that kernel B must know it is > > original kernel (A) or kexeced kernel (B). Different code should be used > > by kernel A and kernel B. And after jump from A to B, jump from B to A, > > when jump from A to B again, kernel A must use different code from the > > first time. > > I don't know what the case is for keeping two kernels in memory and switching > between them.
This can be used to save the memory image of kernel B and accelerate the hibernation. The real boot of kernel B is only needed first time.
> I suspect a small piece of trampoline code between the two kernels could > handle the case. (i.e. purgatory pays attention). > > That is a fundamental aspect of the design. A general purpose infrastructure > with trampoline code to adapt it to whatever situation comes up.
It is possible to use purgatory to deal with this problem.
Jump from kernel A to kernel B Jump to entry of purgatory (purgatory_entry) purgatory save the return address (kexec_jump_back_entry_A) Purgatory set kexec_jump_back_entry for kernel B to a code segment in purgatory, say kexec_jump_back_entry_A_for_B Purgatory jump to entry point of kernel B Jump from kernel B to kernel A Jump to purgatory (kexec_jump_back_entry_A_for_B) Purgatory save the return address (kexec_jump_back_entry_B) Purgatory return to kernel A (kexec_jump_back_entry_A) Jump from kernel A to kernel B again Jump to entry of purgatory (purgatory_entry) Purgatory save the return address (kexec_jump_back_entry_A) Purgatory jump to kexec_jump_back_entry_B
The disadvantage of this solution is that some information is saved in purgatory (kexec_jump_back_entry_A, kexec_jump_back_entry_B). So, purgatory must be saved too when save the memory image of kernel A or kernel B. Purgatory can be seen as a part of kernel B. But it is a little tricky to think it as a part of kernel A too.
Best Regards, Huang Ying
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