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    SubjectRe: [PATCH 00/24] KVM: x86/mmu: Introduce MMU_PRESENT and fix bugs
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    On 25/02/21 21:47, Sean Christopherson wrote:
    > This series adds the simple idea of tagging shadow-present SPTEs with
    > a single bit, instead of looking for non-zero SPTEs that aren't MMIO and
    > aren't REMOVED. Doing so reduces KVM's code footprint by 2k bytes on
    > x86-64, and presumably adds a tiny performance boost in related paths.
    >
    > But, actually adding MMU_PRESENT without breaking one flow or another is
    > a bit of a debacle. The main issue is that EPT doesn't have many low
    > available bits, and PAE doesn't have any high available bits. And, the
    > existing MMU_WRITABLE and HOST_WRITABLE flags aren't optional, i.e. are
    > needed for all flavors of paging. The solution I settled on is to let
    > make the *_WRITABLE bit configurable so that EPT can use high available
    > bits.
    >
    > Of course, I forgot the above PAE restriction multiple times, and
    > journeyed down several dead ends. The most notable failed idea was
    > using the AD_* masks in bits 52 and 53 to denote shadow-present SPTEs.
    > That would have been quite clever as it would provide the same benefits
    > without burning another available bit.
    >
    > Along the many failed attempts, I collected a variety of bug fixes and
    > cleanups, mostly things found by inspection after doing a deep dive to
    > figure out what I broke.
    >
    > Sean Christopherson (24):
    > KVM: x86/mmu: Set SPTE_AD_WRPROT_ONLY_MASK if and only if PML is
    > enabled
    > KVM: x86/mmu: Check for shadow-present SPTE before querying A/D status
    > KVM: x86/mmu: Bail from fast_page_fault() if SPTE is not
    > shadow-present
    > KVM: x86/mmu: Disable MMIO caching if MMIO value collides with L1TF
    > KVM: x86/mmu: Retry page faults that hit an invalid memslot
    > KVM: x86/mmu: Don't install bogus MMIO SPTEs if MMIO caching is
    > disabled
    > KVM: x86/mmu: Handle MMIO SPTEs directly in mmu_set_spte()
    > KVM: x86/mmu: Drop redundant trace_kvm_mmu_set_spte() in the TDP MMU
    > KVM: x86/mmu: Rename 'mask' to 'spte' in MMIO SPTE helpers
    > KVM: x86/mmu: Stop using software available bits to denote MMIO SPTEs
    > KVM: x86/mmu: Add module param to disable MMIO caching (for testing)
    > KVM: x86/mmu: Rename and document A/D scheme for TDP SPTEs
    > KVM: x86/mmu: Use MMIO SPTE bits 53 and 52 for the MMIO generation
    > KVM: x86/mmu: Document dependency bewteen TDP A/D type and saved bits
    > KVM: x86/mmu: Move initial kvm_mmu_set_mask_ptes() call into MMU
    > proper
    > KVM: x86/mmu: Co-locate code for setting various SPTE masks
    > KVM: x86/mmu: Move logic for setting SPTE masks for EPT into the MMU
    > proper
    > KVM: x86/mmu: Make Host-writable and MMU-writable bit locations
    > dynamic
    > KVM: x86/mmu: Use high bits for host/mmu writable masks for EPT SPTEs
    > KVM: x86/mmu: Use a dedicated bit to track shadow/MMU-present SPTEs
    > KVM: x86/mmu: Tweak auditing WARN for A/D bits to !PRESENT (was MMIO)
    > KVM: x86/mmu: Use is_removed_spte() instead of open coded equivalents
    > KVM: x86/mmu: Use low available bits for removed SPTEs
    > KVM: x86/mmu: Dump reserved bits if they're detected on non-MMIO SPTE
    >
    > Documentation/virt/kvm/locking.rst | 49 +++++----
    > arch/x86/include/asm/kvm_host.h | 3 -
    > arch/x86/kvm/mmu.h | 15 +--
    > arch/x86/kvm/mmu/mmu.c | 87 +++++++---------
    > arch/x86/kvm/mmu/mmu_internal.h | 16 +--
    > arch/x86/kvm/mmu/paging_tmpl.h | 2 +-
    > arch/x86/kvm/mmu/spte.c | 157 ++++++++++++++++++++---------
    > arch/x86/kvm/mmu/spte.h | 135 +++++++++++++++++--------
    > arch/x86/kvm/mmu/tdp_mmu.c | 22 ++--
    > arch/x86/kvm/svm/svm.c | 2 +-
    > arch/x86/kvm/vmx/vmx.c | 24 +----
    > arch/x86/kvm/x86.c | 3 -
    > 12 files changed, 290 insertions(+), 225 deletions(-)
    >

    Queued (patch 1 for 5.12, the rest for 5.13).

    Paolo

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