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Message-ID: <aLlGeLOE_PVsYDAU@linux.dev>
Date: Thu, 4 Sep 2025 00:57:44 -0700
From: Oliver Upton <oliver.upton@...ux.dev>
To: Sascha Bischoff <Sascha.Bischoff@....com>
Cc: "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
"kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>, nd <nd@....com>,
"maz@...nel.org" <maz@...nel.org>, Joey Gouly <Joey.Gouly@....com>,
Suzuki Poulose <Suzuki.Poulose@....com>,
"yuzenghui@...wei.com" <yuzenghui@...wei.com>,
"will@...nel.org" <will@...nel.org>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"lpieralisi@...nel.org" <lpieralisi@...nel.org>,
Timothy Hayes <Timothy.Hayes@....com>
Subject: Re: [PATCH 0/5] KVM: arm64: GICv5 legacy (GCIE_LEGACY) NV enablement
and cleanup
On Thu, Aug 28, 2025 at 10:59:41AM +0000, Sascha Bischoff wrote:
> Hi all,
>
> This series enables nested virtualization for GICv3-based VMs on GICv5
> hosts (w/ FEAT_GCIE_LEGACY) in KVM/arm64. In addition, it adds a CPU
> capability to track support for FEAT_GCIE_LEGACY across all CPUs.
>
> The series fixes ICC_SRE_EL2 access handling for GICv5 hosts (to match
> the updated bet1+ specification [1]), and extends nested
> virtualization support to vGICv3 guests running on compatible GICv5
> systems. With these changes, it becomes possible to run with
> kvm-arm.mode=nested, and these changes have been tested with three
> levels of nesting on simulated hardware (Arm FVP).
>
> Previously, the presence of FEAT_GCIE_LEGACY was tracked in the GICv5
> driver via gic_kvm_info, and the probing logic could incorrectly
> enable legacy support if the boot CPU exposed the feature while others
> did not. This created the risk of mismatched configurations,
> particularly when late-onlining CPUs without FEAT_GCIE_LEGACY.
>
> To address this, the series introduces a proper ARM64_HAS_GICV5_LEGACY
> CPU capability, and moves KVM to use cpus_have_final_cap() to ensure
> consistent system-wide enablement. With this, late-onlined but
> mismatched CPUs are cleanly rejected at bring-up.
>
> Patch summary
>
> KVM: arm64: allow ICC_SRE_EL2 accesses on a GICv5 host
> Update handling to reflect the corrected GICv5 specification.
>
> KVM: arm64: Enable nested for GICv5 host with FEAT_GCIE_LEGACY
> Allow nested virtualization for vGICv3 guests on GICv5 hosts with
> legacy support.
>
> arm64: cpucaps: Add GICv5 Legacy vCPU interface (GCIE_LEGACY) capability
> Introduce a new CPU capability that prevents mismatched
> configurations.
>
> KVM: arm64: Use ARM64_HAS_GICV5_LEGACY for GICv5 probing
> Ensure probing is consistent across all CPUs by using cpucaps.
>
> irqchip/gic-v5: Drop has_gcie_v3_compat from gic_kvm_info
> Remove obsolete compatibility flag, as FEAT_GCIE_LEGACY is now a
> CPU feature.
>
> Comments and reviews are very welcome.
>
> Thanks,
> Sascha
>
> [1] https://developer.arm.com/documentation/aes0070/latest/
>
> Sascha Bischoff (5):
> KVM: arm64: Allow ICC_SRE_EL2 accesses on a GICv5 host
> KVM: arm64: Enable nested for GICv5 host with FEAT_GCIE_LEGACY
> arm64: cpucaps: Add GICv5 Legacy vCPU interface (GCIE_LEGACY)
> capability
> KVM: arm64: Use ARM64_HAS_GICV5_LEGACY for GICv5 probing
> irqchip/gic-v5: Drop has_gcie_v3_compat from gic_kvm_info
For the series:
Reviewed-by: Oliver Upton <oliver.upton@...ux.dev>
Thanks,
Oliver
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