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

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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




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