linux-kernel - [PATCH v2 0/6] KVM: Fold kvm_arch_sched_in() into kvm_arch_vcpu

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Date: Tue, 21 May 2024 18:40:07 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Tianrui Zhao <zhaotianrui@...ngson.cn>, Bibo Mao <maobibo@...ngson.cn>, 
	Huacai Chen <chenhuacai@...nel.org>, Michael Ellerman <mpe@...erman.id.au>, 
	Anup Patel <anup@...infault.org>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Christian Borntraeger <borntraeger@...ux.ibm.com>, Janosch Frank <frankja@...ux.ibm.com>, 
	Claudio Imbrenda <imbrenda@...ux.ibm.com>, Sean Christopherson <seanjc@...gle.com>, 
	Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	kvm@...r.kernel.org, loongarch@...ts.linux.dev, linux-mips@...r.kernel.org, 
	linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/6] KVM: Fold kvm_arch_sched_in() into kvm_arch_vcpu_load()

Drop kvm_arch_sched_in() and instead add and use kvm_vcpu.scheduled_out
to communicate to kvm_arch_vcpu_load() that the vCPU is being scheduling
back in.

While fiddling with an idea for optimizing state management on AMD CPUs,
I wanted to skip re-saving certain host state when a vCPU is scheduled back
in, as the state (theoretically) shouldn't change for the task while it's
scheduled out.  Actually doing that was annoying and unnecessarily brittle
due to having a separate API for the kvm_sched_in() case (the state save
needed to be in kvm_arch_vcpu_load() for the common path).

The other motivation for this is to avoid yet another arch hook, and more
arbitrary ordering, if there's a future need to hook kvm_sched_out() (we've
come close on the x86 side several times).  E.g. kvm_arch_vcpu_put() can
simply check kvm_vcpu.scheduled_out if it needs to something specific for
the vCPU being scheduled out.

v2:
 - Add scheduled_out flag instead of passing a bool to kvm_arch_vcpu_load().
   [Oliver]
 - Tack on patches to clean up x86's setting of l1tf_flush_l1d in
   kvm_arch_sched_load() (the code looked slightly less weird when the flag
   was being set by kvm_arch_sched_in()).

v1: https://lore.kernel.org/all/20240430193157.419425-1-seanjc@google.com

Sean Christopherson (6):
  KVM: Add a flag to track if a loaded vCPU is scheduled out
  KVM: VMX: Move PLE grow/shrink helpers above vmx_vcpu_load()
  KVM: x86: Fold kvm_arch_sched_in() into kvm_arch_vcpu_load()
  KVM: Delete the now unused kvm_arch_sched_in()
  KVM: x86: Unconditionally set l1tf_flush_l1d during vCPU load
  KVM: x86: Drop now-superflous setting of l1tf_flush_l1d in vcpu_run()

 arch/arm64/include/asm/kvm_host.h     |  1 -
 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     |  1 -
 arch/s390/include/asm/kvm_host.h      |  1 -
 arch/x86/include/asm/kvm-x86-ops.h    |  1 -
 arch/x86/include/asm/kvm_host.h       |  2 -
 arch/x86/kvm/pmu.c                    |  6 +-
 arch/x86/kvm/svm/svm.c                | 11 +---
 arch/x86/kvm/vmx/main.c               |  2 -
 arch/x86/kvm/vmx/vmx.c                | 80 +++++++++++++--------------
 arch/x86/kvm/vmx/x86_ops.h            |  1 -
 arch/x86/kvm/x86.c                    | 22 +++-----
 include/linux/kvm_host.h              |  3 +-
 virt/kvm/kvm_main.c                   |  5 +-
 16 files changed, 59 insertions(+), 80 deletions(-)


base-commit: 4aad0b1893a141f114ba40ed509066f3c9bc24b0
-- 
2.45.0.215.g3402c0e53f-goog