Re: [PATCH v7 4/8] KVM: x86/mmu: Migrate to __kvm_follow_pfn

[Yu Zhang <yu.c.zhang@linux.intel.com>]

On Tue, Jul 04, 2023 at 04:50:49PM +0900, David Stevens wrote:
> From: David Stevens <stevensd@chromium.org>
> 
> Migrate from __gfn_to_pfn_memslot to __kvm_follow_pfn.
> 
> Signed-off-by: David Stevens <stevensd@chromium.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))
> +		goto success;
> +
> +	if (fault->pfn != KVM_PFN_ERR_NEEDS_IO)
> +		return RET_PF_CONTINUE;

IIUC, FOLL_NOWAIT is set only when we wanna an async fault. So
KVM_PFN_ERR_NEEDS_IO may not be necessary? 

B.R.
Yu