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Date: Tue, 29 Apr 2025 15:09:54 +0100
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Subject: Re: [PATCH v3 24/42] KVM: arm64: Unconditionally configure fine-grain
 traps
To: Marc Zyngier <maz@kernel.org>
Cc: kvmarm@lists.linux.dev, kvm@vger.kernel.org,
 linux-arm-kernel@lists.infradead.org, Joey Gouly <joey.gouly@arm.com>,
 Suzuki K Poulose <suzuki.poulose@arm.com>,
 Oliver Upton <oliver.upton@linux.dev>, Zenghui Yu <yuzenghui@huawei.com>,
 Mark Rutland <mark.rutland@arm.com>, Fuad Tabba <tabba@google.com>,
 Will Deacon <will@kernel.org>, Catalin Marinas <catalin.marinas@arm.com>
References: <20250426122836.3341523-1-maz@kernel.org>
 <20250426122836.3341523-25-maz@kernel.org>
 <363383a2-c05e-458c-82b7-acc6e5d73939@arm.com> <86h627hyby.wl-maz@kernel.org>
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From: Ben Horgan <ben.horgan@arm.com>
In-Reply-To: <86h627hyby.wl-maz@kernel.org>
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On 4/29/25 14:49, Marc Zyngier wrote:
> On Tue, 29 Apr 2025 14:08:27 +0100,
> Ben Horgan <ben.horgan@arm.com> wrote:
>>>    -	__deactivate_fgt(hctxt, vcpu, kvm, HFGRTR_EL2);
>>> -	if (cpus_have_final_cap(ARM64_WORKAROUND_AMPERE_AC03_CPU_38))
>> Don't we need to continue considering the ampere errata here? Or, at
>> least worth a mention in the commit message.
> 
> The FGT registers are always context switched, so whatever was saved
> *before* the workaround was applied in __activate_traps_hfgxtr() is
> blindly restored...
> 
>>> -		write_sysreg_s(ctxt_sys_reg(hctxt, HFGWTR_EL2), SYS_HFGWTR_EL2);
> 
> ... and this write always happens.
Thanks for the explanation. I now agree this code is correct.
> 
> 	M.
> 

Thanks,

Ben