Re: [PATCH v2 4/6] KVM: arm64: add emulation for CTR_EL0 register

From: Oliver Upton <oliver.upton@linux.dev>
To: Sebastian Ott <sebott@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	linux-kernel@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>
Subject: Re: [PATCH v2 4/6] KVM: arm64: add emulation for CTR_EL0 register
Date: Wed, 8 May 2024 12:18:43 -0500	[thread overview]
Message-ID: <Zjuz87jRcrHXebpx@linux.dev> (raw)
In-Reply-To: <29e7b97b-7a61-9b64-2c57-5a5d0e5f190e@redhat.com>

On Wed, May 08, 2024 at 05:17:25PM +0200, Sebastian Ott wrote:
> Hej Oliver,
> 
> On Wed, 1 May 2024, Oliver Upton wrote:
> > > +static u64 reset_ctr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd)
> > > +{
> > > +	vcpu->kvm->arch.ctr_el0 = read_sanitised_ftr_reg(SYS_CTR_EL0);
> > > +	return vcpu->kvm->arch.ctr_el0;
> > > +}
> > > +
> > 
> > We definitely do not want this value to change across a vCPU reset, it
> > should be handled like the other ID registers where they only get reset
> > once for the VM lifetime.
> 
> Hm, maybe I'm misreading the code here but I don't think this is true
> for existing regs e.g. CLIDR_EL1 or the stuff defined via ID_WRITABLE().

This works for the feature ID registers we maintain per-VM, but not for
the feature ID registers local to a vCPU. Sent some fixes out for this
but forgot to Cc you on it, apologies.

https://lore.kernel.org/kvmarm/20240502233529.1958459-1-oliver.upton@linux.dev/

-- 
Thanks,
Oliver