Re: [PATCH 0/6] KVM: Remove uses of struct page from x86 and arm64 MMU

From: Paolo Bonzini <pbonzini@redhat.com>
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>
Subject: Re: [PATCH 0/6] KVM: Remove uses of struct page from x86 and arm64 MMU
Date: Thu, 24 Jun 2021 08:57:37 +0200	[thread overview]
Message-ID: <20baae77-785c-5d46-e00c-41d86c2fbc56@redhat.com> (raw)
In-Reply-To: <20210624035749.4054934-1-stevensd@google.com>

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