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[0/7] KVM: x86: nVMX IRQ fix and VM teardown cleanups

Message ID 20250224235542.2562848-1-seanjc@google.com (mailing list archive)
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Series KVM: x86: nVMX IRQ fix and VM teardown cleanups | expand

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Sean Christopherson Feb. 24, 2025, 11:55 p.m. UTC 
This was _supposed_ to be a tiny one-off patch to fix a nVMX bug where KVM
fails to detect that, after nested VM-Exit, L1 has a pending IRQ (or NMI).
But because x86's nested teardown flows are garbage (KVM simply forces a
nested VM-Exit to put the vCPU back into L1), that simple fix snowballed.

The immediate issue is that checking for a pending interrupt accesses the
legacy PIC, and x86's kvm_arch_destroy_vm() currently frees the PIC before
destroying vCPUs, i.e. checking for IRQs during the forced nested VM-Exit
results in a NULL pointer deref (or use-after-free if KVM didn't nullify
the PIC pointer).  That's patch 1.

Patch 2 is the original nVMX fix.

The remaining patches attempt to bring a bit of sanity to x86's VM
teardown code, which has accumulated a lot of cruft over the years.  E.g.
KVM currently unloads each vCPU's MMUs in a separate operation from
destroying vCPUs, all because when guest SMP support was added, KVM had a
kludgy MMU teardown flow that broken when a VM had more than one 1 vCPU.
And that oddity lived on, for 18 years...

Sean Christopherson (7):
  KVM: x86: Free vCPUs before freeing VM state
  KVM: nVMX: Process events on nested VM-Exit if injectable IRQ or NMI
    is pending
  KVM: Assert that a destroyed/freed vCPU is no longer visible
  KVM: x86: Don't load/put vCPU when unloading its MMU during teardown
  KVM: x86: Unload MMUs during vCPU destruction, not before
  KVM: x86: Fold guts of kvm_arch_sync_events() into
    kvm_arch_pre_destroy_vm()
  KVM: Drop kvm_arch_sync_events() now that all implementations are nops

 arch/arm64/include/asm/kvm_host.h     |  2 --
 arch/loongarch/include/asm/kvm_host.h |  1 -
 arch/mips/include/asm/kvm_host.h      |  1 -
 arch/powerpc/include/asm/kvm_host.h   |  1 -
 arch/riscv/include/asm/kvm_host.h     |  2 --
 arch/s390/include/asm/kvm_host.h      |  1 -
 arch/x86/kvm/vmx/nested.c             | 11 +++++++
 arch/x86/kvm/x86.c                    | 42 ++++++++++-----------------
 include/linux/kvm_host.h              |  1 -
 virt/kvm/kvm_main.c                   |  9 +++++-
 10 files changed, 34 insertions(+), 37 deletions(-)


base-commit: fed48e2967f402f561d80075a20c5c9e16866e53