[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <f7cd9b3d-c817-7082-d60a-a529e1c82f1e@redhat.com>
Date: Thu, 19 Oct 2023 12:45:30 +0200 (CEST)
From: Sebastian Ott <sebott@...hat.com>
To: Raghavendra Rao Ananta <rananta@...gle.com>
cc: Oliver Upton <oliver.upton@...ux.dev>,
Marc Zyngier <maz@...nel.org>,
Alexandru Elisei <alexandru.elisei@....com>,
James Morse <james.morse@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Paolo Bonzini <pbonzini@...hat.com>,
Zenghui Yu <yuzenghui@...wei.com>,
Shaoqin Huang <shahuang@...hat.com>,
Jing Zhang <jingzhangos@...gle.com>,
Reiji Watanabe <reijiw@...gle.com>,
Colton Lewis <coltonlewis@...gle.com>,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v7 08/12] KVM: arm64: PMU: Allow userspace to limit
PMCR_EL0.N for the guest
On Tue, 17 Oct 2023, Raghavendra Rao Ananta wrote:
> On Tue, Oct 17, 2023 at 8:52 AM Sebastian Ott <sebott@...hat.com> wrote:
>>
>> On Mon, 9 Oct 2023, Raghavendra Rao Ananta wrote:
>>> +static int set_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
>>> + u64 val)
>>> +{
>>> + struct kvm *kvm = vcpu->kvm;
>>> + u64 new_n, mutable_mask;
>>> +
>>> + mutex_lock(&kvm->arch.config_lock);
>>> +
>>> + /*
>>> + * Make PMCR immutable once the VM has started running, but do
>>> + * not return an error (-EBUSY) to meet the existing expectations.
>>> + */
>>
>> Why should we mention which error we're _not_ returning?
>>
> Oh, it's not to break the existing userspace expectations. Before this
> series, any 'write' from userspace was possible. Returning -EBUSY all
> of a sudden might tamper with this expectation.
Yes I get that part. What I've meant is why specifically mention -EBUSY?
You're also not returning -EFAULT nor -EINVAL.
/*
* Make PMCR immutable once the VM has started running, but do
* not return an error to meet the existing expectations.
*/
IMHO provides the same info to the reader and is less confusing
Sebastian
Powered by blists - more mailing lists