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Date:   Thu, 24 Jun 2021 18:52:06 +1000
From:   Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH 2/6] KVM: mmu: also return page from gfn_to_pfn
To:     Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
        Huacai Chen <chenhuacai@kernel.org>,
        Marc Zyngier <maz@kernel.org>,
        Paul Mackerras <paulus@ozlabs.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        David Stevens <stevensd@chromium.org>,
        Zhenyu Wang <zhenyuw@linux.intel.com>,
        Zhi Wang <zhi.a.wang@intel.com>
Cc:     Alexandru Elisei <alexandru.elisei@arm.com>,
        dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,
        intel-gvt-dev@lists.freedesktop.org,
        James Morse <james.morse@arm.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvmarm@lists.cs.columbia.edu,
        kvm-ppc@vger.kernel.org, kvm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        Sean Christopherson <seanjc@google.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Will Deacon <will@kernel.org>
References: <20210624035749.4054934-1-stevensd@google.com>
        <20210624035749.4054934-3-stevensd@google.com>
In-Reply-To: <20210624035749.4054934-3-stevensd@google.com>
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Excerpts from David Stevens's message of June 24, 2021 1:57 pm:
> From: David Stevens <stevensd@chromium.org>
>=20
> Return a struct kvm_pfn_page containing both a pfn and an optional
> struct page from the gfn_to_pfn family of functions. This differentiates
> the gup and follow_fault_pfn cases, which allows callers that only need
> a pfn to avoid touching the page struct in the latter case. For callers
> that need a struct page, introduce a helper function that unwraps a
> struct kvm_pfn_page into a struct page. This helper makes the call to
> kvm_get_pfn which had previously been in hva_to_pfn_remapped.
>=20
> For now, wrap all calls to gfn_to_pfn functions in the new helper
> function. Callers which don't need the page struct will be updated in
> follow-up patches.

Hmm. You mean callers that do need the page will be updated? Normally=20
if there will be leftover users that don't need the struct page then
you would go the other way and keep the old call the same, and add a new
one (gfn_to_pfn_page) just for those that need it.

Most kernel code I look at passes back multiple values by updating=20
pointers to struct or variables rather than returning a struct, I=20
suppose that's not really a big deal and a matter of taste.

Thanks,
Nick