linux-kernel - Re: [PATCH 15/24] kvm: mmu: Wrap mmu_lock cond

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Date:   Thu, 28 Jan 2021 09:18:02 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <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 15/24] kvm: mmu: Wrap mmu_lock cond_resched and needbreak

On 27/01/21 22:20, Ben Gardon wrote:
> On Wed, Jan 27, 2021 at 12:55 PM Paolo Bonzini <pbonzini@...hat.com> wrote:
>>
>> On 27/01/21 21:08, Ben Gardon wrote:
>>> I'm not entirely sure I understand this suggestion. Are you suggesting
>>> we'd have the spinlock and rwlock in a union in struct kvm but then
>>> use a static define to choose which one is used by other functions? It
>>> seems like if we're using static defines the union doesn't add value.
>>
>> Of course you're right.  You'd just place the #ifdef in the struct kvm
>> definition.
> 
> Ah okay, thanks for clarifying.
> 
>>
>> You can place static inline functions for lock/unlock in
>> virt/kvm/mmu_lock.h, in order to avoid a proliferation of #ifdefs.
> 
> Would you prefer to make that change in this series or at a later
> date? I'm assuming this would replace all the wrapper functions and
> mean that x86 is rwlock only.

Yes, exactly.  I would like to make tdp_mmu=1 the default as soon as 
parallel page faults are in (and thus scalability should be on par with 
the shadow MMU).

Paolo