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Subject: Re: [PATCH 0/6] KVM: Remove uses of struct page from x86 and arm64
 MMU
To:     David Stevens <stevensd@chromium.org>,
        Marc Zyngier <maz@kernel.org>,
        Huacai Chen <chenhuacai@kernel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
        Paul Mackerras <paulus@ozlabs.org>,
        Zhenyu Wang <zhenyuw@linux.intel.com>,
        Zhi Wang <zhi.a.wang@intel.com>
Cc:     James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Will Deacon <will@kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
        kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, intel-gvt-dev@lists.freedesktop.org,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        David Stevens <stevensd@google.com>
References: <20210624035749.4054934-1-stevensd@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20baae77-785c-5d46-e00c-41d86c2fbc56@redhat.com>
Date:   Thu, 24 Jun 2021 08:57:37 +0200
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On 24/06/21 05:57, David Stevens wrote:
> KVM supports mapping VM_IO and VM_PFNMAP memory into the guest by using
> follow_pte in gfn_to_pfn. However, the resolved pfns may not have
> assoicated struct pages, so they should not be passed to pfn_to_page.
> This series removes such calls from the x86 and arm64 secondary MMU. To
> do this, this series modifies gfn_to_pfn to return a struct page in
> addition to a pfn, if the hva was resolved by gup. This allows the
> caller to call put_page only when necessated by gup.
> 
> This series provides a helper function that unwraps the new return type
> of gfn_to_pfn to provide behavior identical to the old behavior. As I
> have no hardware to test powerpc/mips changes, the function is used
> there for minimally invasive changes. Additionally, as gfn_to_page and
> gfn_to_pfn_cache are not integrated with mmu notifier, they cannot be
> easily changed over to only use pfns.
> 
> This addresses CVE-2021-22543 on x86 and arm64.

Thank you very much for this.  I agree that it makes sense to have a 
minimal change; I had similar changes almost ready, but was stuck with 
deadlocks in the gfn_to_pfn_cache case.  In retrospect I should have 
posted something similar to your patches.

I have started reviewing the patches, and they look good.  I will try to 
include them in 5.13.

Paolo