linux-kernel - Re: [PATCH v7 4/8] KVM: x86/mmu: Migrate to __kvm_follow

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Message-ID: <20230706015449.GB3894444@ls.amr.corp.intel.com>
Date:   Wed, 5 Jul 2023 18:54:49 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     David Stevens <stevensd@...omium.org>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Peter Xu <peterx@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm@...r.kernel.org, isaku.yamahata@...il.com
Subject: Re: [PATCH v7 4/8] KVM: x86/mmu: Migrate to __kvm_follow_pfn

On Tue, Jul 04, 2023 at 04:50:49PM +0900,
David Stevens <stevensd@...omium.org> wrote:

> From: David Stevens <stevensd@...omium.org>
> 
> Migrate from __gfn_to_pfn_memslot to __kvm_follow_pfn.
> 
> Signed-off-by: David Stevens <stevensd@...omium.org>
> ---
>  arch/x86/kvm/mmu/mmu.c | 35 +++++++++++++++++++++++++----------
>  1 file changed, 25 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index ec169f5c7dce..e44ab512c3a1 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4296,7 +4296,12 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
>  static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>  {
>  	struct kvm_memory_slot *slot = fault->slot;
> -	bool async;
> +	struct kvm_follow_pfn foll = {
> +		.slot = slot,
> +		.gfn = fault->gfn,
> +		.flags = FOLL_GET | (fault->write ? FOLL_WRITE : 0),
> +		.allow_write_mapping = true,
> +	};
>  
>  	/*
>  	 * Retry the page fault if the gfn hit a memslot that is being deleted
> @@ -4325,12 +4330,14 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
>  			return RET_PF_EMULATE;
>  	}
>  
> -	async = false;
> -	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async,
> -					  fault->write, &fault->map_writable,
> -					  &fault->hva);
> -	if (!async)
> -		return RET_PF_CONTINUE; /* *pfn has correct page already */
> +	foll.flags |= FOLL_NOWAIT;
> +	fault->pfn = __kvm_follow_pfn(&foll);
> +
> +	if (!is_error_noslot_pfn(fault->pfn))

We have pfn in struct kvm_follow_pfn as output. Can we make __kvm_follow_pfn()
return int instead of kvm_pfn_t?  KVM_PFN_* seems widely used, though.


> +		goto success;
> +
> +	if (fault->pfn != KVM_PFN_ERR_NEEDS_IO)
> +		return RET_PF_CONTINUE;
>  
>  	if (!fault->prefetch && kvm_can_do_async_pf(vcpu)) {
>  		trace_kvm_try_async_get_page(fault->addr, fault->gfn);
> @@ -4348,9 +4355,17 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
>  	 * to wait for IO.  Note, gup always bails if it is unable to quickly
>  	 * get a page and a fatal signal, i.e. SIGKILL, is pending.
>  	 */
> -	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, true, NULL,
> -					  fault->write, &fault->map_writable,
> -					  &fault->hva);
> +	foll.flags |= FOLL_INTERRUPTIBLE;
> +	foll.flags &= ~FOLL_NOWAIT;
> +	fault->pfn = __kvm_follow_pfn(&foll);
> +
> +	if (!is_error_noslot_pfn(fault->pfn))
> +		goto success;
> +
> +	return RET_PF_CONTINUE;
> +success:
> +	fault->hva = foll.hva;
> +	fault->map_writable = foll.writable;
>  	return RET_PF_CONTINUE;
>  }
>  
> -- 
> 2.41.0.255.g8b1d071c50-goog
> 

-- 
Isaku Yamahata <isaku.yamahata@...il.com>