[v2,0/6] KVM: Fold kvm_arch_sched_in() into kvm_arch_vcpu_load()

Message

Sean Christopherson May 22, 2024, 1:40 a.m. UTC

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/[e-mail]

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

Comments

Kai Huang May 23, 2024, 10:48 p.m. UTC | #1

On 22/05/2024 1:40 pm, Sean Christopherson wrote:
> 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.
> 

For this series,

Acked-by: Kai Huang <[e-mail]>

Sean Christopherson June 12, 2024, 1:18 a.m. UTC | #2

On Tue, 21 May 2024 18:40:07 -0700, Sean Christopherson wrote:
> 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).
> 
> [...]

Applied to kvm-x86 generic, thanks!

[1/6] KVM: Add a flag to track if a loaded vCPU is scheduled out
      https://github.com/kvm-x86/linux/commit/d1ae567fb8b5
[2/6] KVM: VMX: Move PLE grow/shrink helpers above vmx_vcpu_load()
      https://github.com/kvm-x86/linux/commit/5d9c07febb86
[3/6] KVM: x86: Fold kvm_arch_sched_in() into kvm_arch_vcpu_load()
      https://github.com/kvm-x86/linux/commit/8fbb696a8f53
[4/6] KVM: Delete the now unused kvm_arch_sched_in()
      https://github.com/kvm-x86/linux/commit/2a27c4314007
[5/6] KVM: x86: Unconditionally set l1tf_flush_l1d during vCPU load
      https://github.com/kvm-x86/linux/commit/ef2e18ef3750
[6/6] KVM: x86: Drop now-superflous setting of l1tf_flush_l1d in vcpu_run()
      https://github.com/kvm-x86/linux/commit/3dee3b187499

--
https://github.com/kvm-x86/linux/tree/next