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

Sean Christopherson
2022-03-11T03:28:07Z

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 (I truly
thought this series was finished 10 commits and 3 days ago...).

Nothing in here is all that urgent; all bugs tagged for stable have been
around for multiple releases (years in most cases).

Sean Christopherson (21):
KVM: x86: Return immediately from x86_emulate_instruction() on code
#DB
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: 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 | 33 +-
arch/x86/kvm/emulate.c | 3 +-
arch/x86/kvm/svm/nested.c | 100 ++---
arch/x86/kvm/svm/svm.c | 18 +-
arch/x86/kvm/vmx/nested.c | 322 +++++++++-----
arch/x86/kvm/vmx/sgx.c | 2 +-
arch/x86/kvm/vmx/vmx.c | 53 ++-
arch/x86/kvm/x86.c | 409 ++++++++++++------
arch/x86/kvm/x86.h | 10 +-
tools/testing/selftests/kvm/.gitignore | 1 +
tools/testing/selftests/kvm/Makefile | 1 +
.../selftests/kvm/include/x86_64/svm_util.h | 5 +-
.../selftests/kvm/include/x86_64/vmx.h | 51 +--
.../kvm/x86_64/nested_exceptions_test.c | 307 +++++++++++++
15 files changed, 914 insertions(+), 403 deletions(-)
create mode 100644 tools/testing/selftests/kvm/x86_64/nested_exceptions_test.c

base-commit: 4a204f7895878363ca8211f50ec610408c8c70aa
--
2.35.1.723.g4982287a31-goog