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

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Date:   Mon, 1 Feb 2021 16:19:14 +0100
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Paolo Bonzini <pbonzini@...hat.com>
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 01.02.2021 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.

> Paolo
> 

Maciej