Message-Id: <20250714033649.4024311-1-suleiman@google.com>
Date: Mon, 14 Jul 2025 12:36:46 +0900
From: Suleiman Souhlal <suleiman@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Chao Gao <chao.gao@...el.com>, 
	David Woodhouse <dwmw2@...radead.org>, Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Tzung-Bi Shih <tzungbi@...nel.org>, 
	John Stultz <jstultz@...gle.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	ssouhlal@...ebsd.org, Suleiman Souhlal <suleiman@...gle.com>
Subject: [PATCH v7 0/3] KVM: x86: Include host suspended time in steal time

This series makes it so that the time that the host is suspended is
included in guests' steal time.

When the host resumes from a suspend, the guest thinks any task
that was running during the suspend ran for a long time, even though
the effective run time was much shorter, which can end up having
negative effects with scheduling.

To mitigate this issue, include the time that the host was
suspended in steal time, if the guest requests it, which lets the
guest subtract the duration from the tasks' runtime. Add new ABI 
to make this behavior opt-in per-guest.

In addition, make the guest TSC behavior consistent whether the
host TSC went backwards or not.

v7:
- Fix build.
- Make advancing TSC dependent on X86_64.

v6: https://lore.kernel.org/kvm/20250709070450.473297-1-suleiman@google.com/
- Use true/false for bools.
- Indentation.
- Remove superfluous flag. 
- Use atomic operations for accumulating suspend duration.
- Reuse generic vcpu block/kick infrastructure instead of rolling our own.
- Add ABI to make the behavior opt-in per-guest.
- Add command line parameter to make guest use this.
- Reword commit messages in imperative mood.

v5: https://lore.kernel.org/kvm/20250325041350.1728373-1-suleiman@google.com/
- Fix grammar mistakes in commit message.

v4: https://lore.kernel.org/kvm/20250221053927.486476-1-suleiman@google.com/
- Advance guest TSC on suspends where host TSC goes backwards.
- Block vCPUs from running until resume notifier.
- Move suspend duration accounting out of machine-independent kvm to
  x86.
- Merge code and documentation patches.
- Reworded documentation.

v3: https://lore.kernel.org/kvm/20250107042202.2554063-1-suleiman@google.com/
- Use PM notifier instead of syscore ops (kvm_suspend()/kvm_resume()),
  because the latter doesn't get called on shallow suspend.
- Don't call function under UACCESS.
- Whitespace.

v2: https://lore.kernel.org/kvm/20240820043543.837914-1-suleiman@google.com/
- Accumulate suspend time at machine-independent kvm layer and track per-VCPU
  instead of per-VM.
- Document changes.

v1: https://lore.kernel.org/kvm/20240710074410.770409-1-suleiman@google.com/

Suleiman Souhlal (3):
  KVM: x86: Advance guest TSC after deep suspend.
  KVM: x86: Include host suspended duration in steal time
  KVM: x86: Add "suspendsteal" cmdline to request host to add suspend
    duration in steal time

 .../admin-guide/kernel-parameters.txt         |   5 +
 Documentation/virt/kvm/x86/cpuid.rst          |   4 +
 Documentation/virt/kvm/x86/msr.rst            |  14 +++
 arch/x86/include/asm/kvm_host.h               |   6 +
 arch/x86/include/uapi/asm/kvm_para.h          |   2 +
 arch/x86/kernel/kvm.c                         |  15 +++
 arch/x86/kvm/cpuid.c                          |   4 +-
 arch/x86/kvm/x86.c                            | 112 +++++++++++++++++-
 8 files changed, 156 insertions(+), 6 deletions(-)

-- 
2.50.0.727.gbf7dc18ff4-goog

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