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Venkatesh Srinivas
ce40908617
[ Upstream commite800decd9c] On Intel platforms with a VMX preemption timer and APICv, if a VMM calls KVM_GET_LAPIC before KVM_GET_MSRS to save the vCPU state, it is possible to lose a pending timer interrupt. If the thread running these ioctls is migrated to another core after calling KVM_GET_LAPIC but before KVM_GET_MSRS and the guest is using their LAPIC timer in TSC-deadline mode, not only does the save LAPIC state not carry the pending interrupt, the TSCDEADLINE MSR will be zeroed. After migration across CPUs, KVM_GET_MSRS calls vcpu_load, posting the interrupt and clearing the MSR: vcpu_load() -> kvm_arch_vcpu_load() -> kvm_lapic_restart_hv_timer() -> start_hv_timer() -> apic_timer_expired() -> kvm_apic_inject_pending_timer_irqs() . post interrupt into the LAPIC state . clear IA32_TSCDEADLINE The saved LAPIC state will be missing the pending interrupt and the saved MSR will be zero. Oops. Fix by only posting an interrupt when we're attempting to enter the guest (vcpu->wants_to_run == true), not for vcpu_load from other paths. Assisted-by: gemini:gemini-3.1-pro-preview Debugged-by: David Matlack <dmatlack@google.com> Debugged-by: Sean Christopherson <seanjc@google.com> Debugged-by: Jim Mattson <jmattson@google.com> Debugged-by: James Houghton <jthoughton@google.com> Signed-off-by: Venkatesh Srinivas <venkateshs@chromium.org> Message-ID: <20260715234234.15382-2-venkateshs@chromium.org> Reviewed-by: James Houghton <jthoughton@google.com> Reviewed-by: Chao Gao <chao.gao@intel.com> Cc: stable@vger.kernel.org Fixes:ae95f566b3("KVM: X86: TSCDEADLINE MSR emulation fastpath", 2020-05-15) Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.