Re: [PATCH v2 00/21] KVM: x86: Event/exception fixes and cleanups

[Maxim Levitsky]

On Tue, 2022-06-14 at 20:47 +0000, Sean Christopherson wrote:
> The main goal of this series is to fix KVM's longstanding bug of not
> honoring L1's exception intercepts wants when handling an exception that
> occurs during delivery of a different exception.  E.g. if L0 and L1 are
> using shadow paging, and L2 hits a #PF, and then hits another #PF while
> vectoring the first #PF due to _L1_ not having a shadow page for the IDT,
> KVM needs to check L1's intercepts before morphing the #PF => #PF => #DF
> so that the #PF is routed to L1, not injected into L2 as a #DF.
> 
> nVMX has hacked around the bug for years by overriding the #PF injector
> for shadow paging to go straight to VM-Exit, and nSVM has started doing
> the same.  The hacks mostly work, but they're incomplete, confusing, and
> lead to other hacky code, e.g. bailing from the emulator because #PF
> injection forced a VM-Exit and suddenly KVM is back in L1.
> 
> Everything leading up to that are related fixes and cleanups I encountered
> along the way; some through code inspection, some through tests.
> 
> v2:
>   - Rebased to kvm/queue (commit 8baacf67c76c) + selftests CPUID
>     overhaul.
>     https://lore.kernel.org/all/20220614200707.3315957-1-seanjc@xxxxxxxxxx
>   - Treat KVM_REQ_TRIPLE_FAULT as a pending exception.
> 
> v1: https://lore.kernel.org/all/20220311032801.3467418-1-seanjc@xxxxxxxxxx
> 
> Sean Christopherson (21):
>   KVM: nVMX: Unconditionally purge queued/injected events on nested
>     "exit"
>   KVM: VMX: Drop bits 31:16 when shoving exception error code into VMCS
>   KVM: x86: Don't check for code breakpoints when emulating on exception
>   KVM: nVMX: Treat General Detect #DB (DR7.GD=1) as fault-like
>   KVM: nVMX: Prioritize TSS T-flag #DBs over Monitor Trap Flag
>   KVM: x86: Treat #DBs from the emulator as fault-like (code and
>     DR7.GD=1)
>   KVM: x86: Use DR7_GD macro instead of open coding check in emulator
>   KVM: nVMX: Ignore SIPI that arrives in L2 when vCPU is not in WFS
>   KVM: nVMX: Unconditionally clear mtf_pending on nested VM-Exit
>   KVM: VMX: Inject #PF on ENCLS as "emulated" #PF
>   KVM: x86: Rename kvm_x86_ops.queue_exception to inject_exception
>   KVM: x86: Make kvm_queued_exception a properly named, visible struct
>   KVM: x86: Formalize blocking of nested pending exceptions
>   KVM: x86: Use kvm_queue_exception_e() to queue #DF
>   KVM: x86: Hoist nested event checks above event injection logic
>   KVM: x86: Evaluate ability to inject SMI/NMI/IRQ after potential
>     VM-Exit
>   KVM: x86: Morph pending exceptions to pending VM-Exits at queue time
>   KVM: x86: Treat pending TRIPLE_FAULT requests as pending exceptions
>   KVM: VMX: Update MTF and ICEBP comments to document KVM's subtle
>     behavior
>   KVM: selftests: Use uapi header to get VMX and SVM exit reasons/codes
>   KVM: selftests: Add an x86-only test to verify nested exception
>     queueing
> 
>  arch/x86/include/asm/kvm-x86-ops.h            |   2 +-
>  arch/x86/include/asm/kvm_host.h               |  35 +-
>  arch/x86/kvm/emulate.c                        |   3 +-
>  arch/x86/kvm/svm/nested.c                     | 102 ++---
>  arch/x86/kvm/svm/svm.c                        |  18 +-
>  arch/x86/kvm/vmx/nested.c                     | 319 +++++++++-----
>  arch/x86/kvm/vmx/sgx.c                        |   2 +-
>  arch/x86/kvm/vmx/vmx.c                        |  53 ++-
>  arch/x86/kvm/x86.c                            | 404 +++++++++++-------
>  arch/x86/kvm/x86.h                            |  11 +-
>  tools/testing/selftests/kvm/.gitignore        |   1 +
>  tools/testing/selftests/kvm/Makefile          |   1 +
>  .../selftests/kvm/include/x86_64/svm_util.h   |   7 +-
>  .../selftests/kvm/include/x86_64/vmx.h        |  51 +--
>  .../kvm/x86_64/nested_exceptions_test.c       | 295 +++++++++++++
>  15 files changed, 886 insertions(+), 418 deletions(-)
>  create mode 100644 tools/testing/selftests/kvm/x86_64/nested_exceptions_test.c
> 
> 
> base-commit: 816967202161955f398ce379f9cbbedcb1eb03cb

Next week I will review all of this patch series.

Best regards,
	Maxim Levitsky