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Date:   Thu, 23 Jun 2022 14:49:47 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Peter Xu <peterx@redhat.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Linux MM Mailing List <linux-mm@kvack.org>
Subject: Re: [PATCH 2/4] kvm: Merge "atomic" and "write" in
 __gfn_to_pfn_memslot()
Message-ID: <YrR9i3yHzh5ftOxB@google.com>
References: <20220622213656.81546-1-peterx@redhat.com>
 <20220622213656.81546-3-peterx@redhat.com>
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In-Reply-To: <20220622213656.81546-3-peterx@redhat.com>
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On Wed, Jun 22, 2022, Peter Xu wrote:
> Merge two boolean parameters into a bitmask flag called kvm_gtp_flag_t for
> __gfn_to_pfn_memslot().  This cleans the parameter lists, and also prepare
> for new boolean to be added to __gfn_to_pfn_memslot().

...

> @@ -3999,8 +4000,8 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>  	}
>  
>  	async = false;
> -	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, &async,
> -					  fault->write, &fault->map_writable,
> +	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, flags,
> +					  &async, &fault->map_writable,
>  					  &fault->hva);
>  	if (!async)
>  		return RET_PF_CONTINUE; /* *pfn has correct page already */
> @@ -4016,9 +4017,8 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>  		}
>  	}
>  
> -	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, NULL,
> -					  fault->write, &fault->map_writable,
> -					  &fault->hva);
> +	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, flags, NULL,
> +					  &fault->map_writable, &fault->hva);
>  	return RET_PF_CONTINUE;
>  }
>  
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index c20f2d55840c..b646b6fcaec6 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1146,8 +1146,15 @@ kvm_pfn_t gfn_to_pfn_prot(struct kvm *kvm, gfn_t gfn, bool write_fault,
>  		      bool *writable);
>  kvm_pfn_t gfn_to_pfn_memslot(const struct kvm_memory_slot *slot, gfn_t gfn);
>  kvm_pfn_t gfn_to_pfn_memslot_atomic(const struct kvm_memory_slot *slot, gfn_t gfn);
> +
> +/* gfn_to_pfn (gtp) flags */
> +typedef unsigned int __bitwise kvm_gtp_flag_t;
> +
> +#define  KVM_GTP_WRITE          ((__force kvm_gtp_flag_t) BIT(0))
> +#define  KVM_GTP_ATOMIC         ((__force kvm_gtp_flag_t) BIT(1))
> +
>  kvm_pfn_t __gfn_to_pfn_memslot(const struct kvm_memory_slot *slot, gfn_t gfn,
> -			       bool atomic, bool *async, bool write_fault,
> +			       kvm_gtp_flag_t gtp_flags, bool *async,
>  			       bool *writable, hva_t *hva);

I completely agree the list of booleans is a mess, but I don't love the result of
adding @flags.  I wonder if we can do something similar to x86's struct kvm_page_fault
and add an internal struct to pass params.  And then add e.g. gfn_to_pfn_interruptible()
to wrap that logic.

I suspect we could also clean up the @async behavior at the same time, as its
interaction with FOLL_NOWAIT is confusing.