From: Oliver Upton <oliver.upton@linux.dev>
To: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <maz@kernel.org>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
kvmarm@lists.linux.dev, Akihiko Odaki <akihiko.odaki@daynix.com>,
Zenghui Yu <yuzenghui@huawei.com>,
Raghavendra Rao Ananta <rananta@google.com>,
linux-arm-kernel@lists.infradead.org,
Salil Mehta <salil.mehta@huawei.com>
Subject: Re: [RFC PATCH v2 5/6] KVM: arm64: Add support for KVM_EXIT_HYPERCALL
Date: Fri, 24 Feb 2023 21:42:48 +0000 [thread overview]
Message-ID: <Y/kvWNH2sIySgudd@linux.dev> (raw)
In-Reply-To: <b10d117a-3d3d-c273-9885-3bfecfa8304d@arm.com>
Hi James,
On Fri, Feb 24, 2023 at 03:12:33PM +0000, James Morse wrote:
> On 11/02/2023 01:37, Oliver Upton wrote:
> > +static void kvm_prepare_hypercall_exit(struct kvm_vcpu *vcpu, u32 func_id, bool smc)
> > +{
> > + struct kvm_run *run = vcpu->run;
> > +
> > + run->exit_reason = KVM_EXIT_HYPERCALL;
>
> > + run->hypercall.nr = func_id;
>
> This is a bit weird. The func_id is the x0 value, so it would more naturally live in
> run->hypercall.args[0].
>
> User-space also needs the SMC/HVC immediate value, as that is only available in the ESR.
> It makes more sense to put the immediate value here.
Completely buy that userspace has no way of getting at the immediate.
But why do we need to expose it in the first place?
The UAPI here has been constructed around SMCCC, so the immediate should
be zero across the board. Sure, SMCCC says that nonzero values can be
used by the hypervisor, but in that case the register interface needn't
follow SMCCC (i.e. what if the function ID is in x7 for some silly
reason).
Curious if there's a use case you had in mind I haven't thought of.
> > + if (smc)
> > + run->hypercall.flags = KVM_HYPERCALL_EXIT_SMC;
Drive by self-review (be warned!): flags needs explicit zeroing,
otherwise this flag will remain up for a subsequent HVC.
--
Thanks,
Oliver
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next prev parent reply other threads:[~2023-02-24 21:43 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-11 1:37 [RFC PATCH v2 0/6] KVM: arm64: Userspace SMCCC call filtering Oliver Upton
2023-02-11 1:37 ` [RFC PATCH v2 1/6] KVM: arm64: Add a helper to check if a VM has ran once Oliver Upton
2023-02-13 15:36 ` Sean Christopherson
2023-02-13 15:49 ` Marc Zyngier
2023-02-11 1:37 ` [RFC PATCH v2 2/6] KVM: arm64: Add vm fd device attribute accessors Oliver Upton
2023-02-11 1:37 ` [RFC PATCH v2 3/6] KVM: arm64: Refactor hvc filtering to support different actions Oliver Upton
2023-02-11 1:37 ` [RFC PATCH v2 4/6] KVM: arm64: Use a maple tree to represent the SMCCC filter Oliver Upton
2023-02-11 1:37 ` [RFC PATCH v2 5/6] KVM: arm64: Add support for KVM_EXIT_HYPERCALL Oliver Upton
2023-02-13 16:01 ` Sean Christopherson
2023-02-13 19:24 ` Oliver Upton
2023-02-24 15:12 ` James Morse
2023-02-24 21:42 ` Oliver Upton [this message]
2023-02-11 1:37 ` [RFC PATCH v2 6/6] KVM: arm64: Indroduce support for userspace SMCCC filtering Oliver Upton
2023-02-17 18:35 ` Oliver Upton
2023-02-24 15:12 ` [RFC PATCH v2 0/6] KVM: arm64: Userspace SMCCC call filtering James Morse
2023-02-24 21:32 ` Oliver Upton
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