[PATCH 00/24] KVM: x86/mmu: Introduce MMU_PRESENT and fix bugs

From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: 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>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Ben Gardon <bgardon@google.com>
Subject: [PATCH 00/24] KVM: x86/mmu: Introduce MMU_PRESENT and fix bugs
Date: Thu, 25 Feb 2021 12:47:25 -0800	[thread overview]
Message-ID: <20210225204749.1512652-1-seanjc@google.com> (raw)

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(-)

-- 
2.30.1.766.gb4fecdf3b7-goog