linux-kernel - Re: [PATCH 04/24] kvm: x86/mmu: change TDP MMU yield function returns to match cond

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Date:   Thu, 21 Jan 2021 21:22:09 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Ben Gardon <bgardon@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Peter Xu <peterx@...hat.com>, Peter Shier <pshier@...gle.com>,
        Peter Feiner <pfeiner@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>
Subject: Re: [PATCH 04/24] kvm: x86/mmu: change TDP MMU yield function returns
 to match cond_resched

On 20/01/21 19:38, Sean Christopherson wrote:
> Currently the TDP MMU yield / cond_resched functions either return
> nothing or return true if the TLBs were not flushed. These are confusing
> semantics, especially when making control flow decisions in calling
> functions.
> 
> To clean things up, change both functions to have the same
> return value semantics as cond_resched: true if the thread yielded,
> false if it did not. If the function yielded in the_flush_  version,
> then the TLBs will have been flushed.

My fault here.  The return value was meant to simplify the assignments 
below.  But it's clearer to return true if the cond_resched happened, 
indeed.

>>
>>  
>>  		if (can_yield)
>> -			flush_needed = tdp_mmu_iter_flush_cond_resched(kvm, &iter);
>> +			flush_needed = !tdp_mmu_iter_flush_cond_resched(kvm,
>> +									&iter);
> 
> As with the existing code, I'd let this poke out.  Alternatively, this could be
> written as:
> 
> 		flush_needed = !can_yield ||
> 			       !tdp_mmu_iter_flush_cond_resched(kvm, &iter);
> 

Yeah, no new line here.

Paolo