From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nicholas Piggin <npiggin@gmail.com>
Date: Thu, 24 Jun 2021 09:57:57 +0000
Subject: Re: [PATCH 2/6] KVM: mmu: also return page from gfn_to_pfn
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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>

Excerpts from Paolo Bonzini's message of June 24, 2021 7:42 pm:
> On 24/06/21 10:52, Nicholas Piggin wrote:
>>> 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
>> 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.
> 
> Needing kvm_pfn_page_unwrap is a sign that something might be buggy, so 
> it's a good idea to move the short name to the common case and the ugly 
> kvm_pfn_page_unwrap(gfn_to_pfn(...)) for the weird one.  In fact I'm not 
> sure there should be any kvm_pfn_page_unwrap in the end.

If all callers were updated that is one thing, but from the changelog
it sounds like that would not happen and there would be some gfn_to_pfn
users left over.

But yes in the end you would either need to make gfn_to_pfn never return
a page found via follow_pte, or change all callers to the new way. If 
the plan is for the latter then I guess that's fine.

Thanks,
Nick