[PATCH v4 00/18] KVM: SEV: Fix RMP #PF due to freeing in-use VMSA

[Sean Christopherson <seanjc@google.com>]

Rework KVM's handling of guest-provided (and always guest_memfd-backed) VMSAs
to forcefully reclaim VMSA pages when the pages are being freed from their
backing gmem instance, e.g. in response to PUNCH_HOLE.  In the worst case
scenario, marking the page SHARED in the RMP will fail due to the page being
IN_USE, ultimately leading to RMP #PF violations due to guest_memfd freeing
the memory back to the kernel while it's still assigned to a VM.

Note, the implementation nearly identical to that used by KVM for VMX's APIC
access page (which isn't guest controlled, but is migratable and whose PA is
shoved directly into a vCPU control structure).

On the backend of the series, rework prepare()+invalidate() into a single
convert() hook, to eliminate the misleading use of the term "invalidate", to
(obviously) drop yet another callback, and to prepare for in-place conversion,
e.g. so that KVM ends up with something like:

	if (!to_private)
		kvm_gmem_make_shared(inode, start, end);

instead of a funky:

	if (!to_private)
		kvm_gmem_invalidate(inode, start, end);

v4:
 - Collect reviews. [Mike, Ackerley]
 - Rework prepare()+invalidate() into a common convert() instead of simply
   renaming invalidate() to reclaim_memory(). [Ackerley]
 - Fix several (mostly benign) issues in the "prepare" flow.

v3:
 - https://lore.kernel.org/all/20260630222607.497895-1-seanjc@google.com
 - Ensure disabling quirks while the VM is live won't result in KVM skipping
   the back-half of "zap all fast". [Sashiko]
 - s/gmem_free_folio/gmem_reclaim_memory. [Ackerley]
 - Use {READ,WRITE}_ONCE() when accessing the guest's VMSA GPA outside of the
   per-vCPU mutex, and comment. [Sashiko]

v2:
 - https://lore.kernel.org/all/20260626231416.3943216-1-seanjc@google.com
 - Invalidate VMSAs if the memslot is DELETED or MOVED. [Sashiko]
 - Limit stable@ patches without a Fixes to 6.12+.

v1: https://lore.kernel.org/all/20260625222229.3367197-2-seanjc@google.com

Sean Christopherson (18):
  KVM: SEV: Track the GPA of the guest-controlled VMSA used for SNP
    guests
  KVM: SEV: Extract loading of guest-provided VMSA to a separate helper
  KVM: SEV: Mark vCPU RUNNABLE after AP_CREATE, even if VMSA is unusable
  KVM: SEV: Wire up kvm_x86_ops.gmem_xxx() if and only if
    CONFIG_KVM_AMD_SEV=y
  KVM: x86: Serialize writes to disabled_quirks using kvm->lock
  KVM: x86: Ensure runtime reads of disabled_quirks are resolved once
  KVM: x86/mmu: Fold kvm_mmu_zap_memslot() into
    kvm_arch_flush_shadow_memslot()
  KVM: x86/mmu: Split kvm_mmu_zap_all_fast() into "front" and "back"
    halves
  KVM: x86/mmu: Use split "zap all fast" helpers when invalidating
    memslot
  KVM: SEV: Forcefully invalidate SNP VMSA if its backing gmem page is
    zapped
  KVM: SEV: Mark vCPU has having guest-provided VMSA even if its invalid
  KVM: x86: Guard .gmem_prepare() declarations with
    HAVE_KVM_GMEM_PREPARE=y
  KVM: guest_memfd: Pass GPA, not GFN, to prepare() hook
  KVM: guest_memfd: Drop the redundant printk on arch gmem_prepare()
    failure
  KVM: guest_memfd: Fold __kvm_gmem_prepare_folio() into its sole caller
  KVM: guest_memfd: Explicitly pass number of pages to
    kvm_arch_gmem_prepare()
  KVM: guest_memfd: Align the gfn as well as the pfn when "preparing" a
    folio
  KVM: guest_memfd: Combine .gmem_prepare()+.gmem_invalidate() into
    .gmem_convert()

 arch/x86/include/asm/kvm-x86-ops.h |   9 +-
 arch/x86/include/asm/kvm_host.h    |  12 +-
 arch/x86/kvm/Kconfig               |   2 +-
 arch/x86/kvm/mmu/mmu.c             |  74 +++++++-----
 arch/x86/kvm/svm/sev.c             | 186 ++++++++++++++++++++++-------
 arch/x86/kvm/svm/svm.c             |   9 +-
 arch/x86/kvm/svm/svm.h             |  19 +--
 arch/x86/kvm/x86.c                 |  21 ++--
 arch/x86/kvm/x86.h                 |   2 +-
 include/linux/kvm_host.h           |   7 +-
 virt/kvm/Kconfig                   |   2 +-
 virt/kvm/guest_memfd.c             |  53 ++++----
 12 files changed, 256 insertions(+), 140 deletions(-)


base-commit: a204badd8432f93b7e862e7dac6db0fe3d65f370
-- 
2.55.0.795.g602f6c329a-goog