linux-kernel - [PATCH 0/4] KVM: Clean up "preempted in-kernel" logic

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Message-ID: <20240110003938.490206-1-seanjc@google.com>
Date: Tue,  9 Jan 2024 16:39:34 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Like Xu <like.xu.linux@...il.com>
Subject: [PATCH 0/4] KVM: Clean up "preempted in-kernel" logic

Provide a dedicated helper to query if a *different* vCPU was preempted
in-kernel.  x86's VMX is an oddball and can only check if the vCPU is in
kernel (versus userspace) if the vCPU is loaded on the current pCPU.

The existing kvm_arch_vcpu_in_kernel() "works", but it's an ugly mess as
KVM x86 is forced to check kvm_get_running_vcpu() to effectively undo the
multiplexing.

Note, I was sorely tempted to eliminate kvm_arch_dy_has_pending_interrupt()
and bury that logic in VMX code, but I ultimately decided to keep it as an
arch hook as it's entirely plausible that some other architecture can do
cross-vCPU IRQ checks, and if KVM is going to have the (somewhat dubious
IMO) logic, it's probably best to keep it in common code.

Sean Christopherson (4):
  KVM: Add dedicated arch hook for querying if vCPU was preempted
    in-kernel
  KVM: x86: Rely solely on preempted_in_kernel flag for directed yield
  KVM: x86: Clean up directed yield API for "has pending interrupt"
  KVM: Add a comment explaining the directed yield pending interrupt
    logic

 arch/x86/kvm/x86.c       | 16 +++++++---------
 include/linux/kvm_host.h |  1 +
 virt/kvm/kvm_main.c      | 22 ++++++++++++++++++++--
 3 files changed, 28 insertions(+), 11 deletions(-)

base-commit: 1c6d984f523f67ecfad1083bb04c55d91977bb15
-- 
2.43.0.472.g3155946c3a-goog