linux-kernel - Re: [PATCH v5 0/5] KVM: arm64: PMU: Fix SET_ONE

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Message-ID: <86a59lnu3d.wl-maz@kernel.org>
Date: Sun, 16 Mar 2025 10:33:10 +0000
From: Marc Zyngier <maz@...nel.org>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Andrew Jones <andrew.jones@...ux.dev>,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	devel@...nix.com,
	stable@...r.kernel.org
Subject: Re: [PATCH v5 0/5] KVM: arm64: PMU: Fix SET_ONE_REG for vPMC regs

On Sat, 15 Mar 2025 09:12:09 +0000,
Akihiko Odaki <akihiko.odaki@...nix.com> wrote:
> 
> Prepare vPMC registers for user-initiated changes after first run. This
> is important specifically for debugging Windows on QEMU with GDB; QEMU
> tries to write back all visible registers when resuming the VM execution
> with GDB, corrupting the PMU state. Windows always uses the PMU so this
> can cause adverse effects on that particular OS.
> 
> This series also contains patch "KVM: arm64: PMU: Set raw values from
> user to PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}", which reverts semantic
> changes made for the mentioned registers in the past. It is necessary
> to migrate the PMU state properly on Firecracker, QEMU, and crosvm.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> ---
> Changes in v5:
> - Rebased.
> - Link to v4: https://lore.kernel.org/r/20250313-pmc-v4-0-2c976827118c@daynix.com
> 
> Changes in v4:
> - Reverted changes for functions implementing ioctls in patch
>   "KVM: arm64: PMU: Assume PMU presence in pmu-emul.c".
> - Removed kvm_pmu_vcpu_reset().
> - Reordered function calls in kvm_vcpu_reload_pmu() for better style.
> - Link to v3: https://lore.kernel.org/r/20250312-pmc-v3-0-0411cab5dc3d@daynix.com
> 
> Changes in v3:
> - Added patch "KVM: arm64: PMU: Assume PMU presence in pmu-emul.c".
> - Added an explanation of this path series' motivation to each patch.
> - Explained why userspace register writes and register reset should be
>   covered in patch "KVM: arm64: PMU: Reload when user modifies
>   registers".
> - Marked patch "KVM: arm64: PMU: Set raw values from user to
>   PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}" for stable.
> - Reoreded so that patch "KVM: arm64: PMU: Set raw values from user to
>   PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}" would come first.
> - Added patch "KVM: arm64: PMU: Call kvm_pmu_handle_pmcr() after masking
>   PMCNTENSET_EL0".
> - Added patch "KVM: arm64: Reload PMCNTENSET_EL0".
> - Link to v2: https://lore.kernel.org/r/20250307-pmc-v2-0-6c3375a5f1e4@daynix.com
> 
> Changes in v2:
> - Changed to utilize KVM_REQ_RELOAD_PMU as suggested by Oliver Upton.
> - Added patch "KVM: arm64: PMU: Reload when user modifies registers"
>   to cover more registers.
> - Added patch "KVM: arm64: PMU: Set raw values from user to
>   PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}".
> - Link to v1: https://lore.kernel.org/r/20250302-pmc-v1-1-caff989093dc@daynix.com
> 
> ---
> Akihiko Odaki (5):
>       KVM: arm64: PMU: Set raw values from user to PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}
>       KVM: arm64: PMU: Assume PMU presence in pmu-emul.c
>       KVM: arm64: PMU: Fix SET_ONE_REG for vPMC regs
>       KVM: arm64: PMU: Reload when user modifies registers
>       KVM: arm64: PMU: Reload when resetting
> 
>  arch/arm64/kvm/arm.c            | 17 ++++++++-----
>  arch/arm64/kvm/emulate-nested.c |  6 +++--
>  arch/arm64/kvm/pmu-emul.c       | 56 +++++++++++------------------------------
>  arch/arm64/kvm/reset.c          |  3 ---
>  arch/arm64/kvm/sys_regs.c       | 52 ++++++++++++++++++++++----------------
>  include/kvm/arm_pmu.h           |  4 +--
>  6 files changed, 62 insertions(+), 76 deletions(-)

Reviewed-by: Marc Zyngier <maz@...nel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.