Re: [PATCH 1/3] kvm/ppc/booke: Hold srcu lock when calling gfn functions

[Scott Wood <scottwood@freescale.com>]

On 05/01/2013 07:27:23 PM, Scott Wood wrote:
> On 05/01/2013 07:15:53 PM, Marcelo Tosatti wrote:
>> This is not good practice (codepaths should either hold srcu or not  
>> hold
>> it, unconditionally).
> 
> How is it different from moving the srcu lock into individual cases  
> of the switch?  I just did it this way to make it easier to add new  
> exception types if necessary (e.g. at the time I thought I'd end up  
> adding exceptions which lead to instruction emulation, but I ended up  
> acquiring the lock further down the path in that case).
> 
>> Can you give more details of the issue? (not obvious)
> 
> ITLB/DTLB miss call things like gfn_to_memslot() which need the lock  
> (but don't grab it themselves -- that seems like the real bad  
> practice here...).

Never mind on the parenthetical -- grabbing it themselves wouldn't work  
because they return RCU-protected data.

-Scott