linux-kernel - Re: [PATCH 1/2] KVM: x86/mmu: Make HVA handler retpoline-friendly

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Message-ID: <7b15ae06-4b56-0259-6950-6781622020ab@redhat.com>
Date:   Wed, 3 Feb 2021 15:43:22 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: x86/mmu: Make HVA handler retpoline-friendly

On 01/02/21 16:19, Maciej S. Szmigiero wrote:
> On 01.02.2021 09:21, Paolo Bonzini wrote:
>> On 01/02/21 09:13, Maciej S. Szmigiero wrote:
>>>   static int kvm_handle_hva_range(struct kvm *kvm,
>>>                   unsigned long start,
>>>                   unsigned long end,
>>> @@ -1495,8 +1534,9 @@ static int kvm_handle_hva_range(struct kvm *kvm,
>>
>>
>>> -static int kvm_tdp_mmu_handle_hva_range(struct kvm *kvm, unsigned 
>>> long start,
>>> -        unsigned long end, unsigned long data,
>>> -        int (*handler)(struct kvm *kvm, struct kvm_memory_slot *slot,
>>> -                   struct kvm_mmu_page *root, gfn_t start,
>>> -                   gfn_t end, unsigned long data))
>>> -{
>>
>> Can you look into just marking these functions __always_inline?  This 
>> should help the compiler change (*handler)(...) into a regular 
>> function call.
> 
> That looks even better - I see the compiler then turns the indirect call
> into a direct one.
> 
> Will change to __always_inline instead of static dispatch in the next
> version.
> Thanks for the pointer.

Feel free to send this separately as it's a self-contained change.

Thanks,

Paolo