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From: Reiji Watanabe <reijiw@google.com>
To: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
	 Will Deacon <will@kernel.org>, Peter Shier <pshier@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	 Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH v4 04/26] KVM: arm64: Make ID_AA64PFR0_EL1 writable
Date: Wed, 9 Feb 2022 21:33:38 -0800	[thread overview]
Message-ID: <CAAeT=FyHGY3ypVQt_P-a8Mj8G_FMUtuwgdhos=DWV1SPeemC7A@mail.gmail.com> (raw)
In-Reply-To: <CA+EHjTzK_We_vwu6QbR3N4J5wJqF00fKm6rf6X8RA_4Mjg=VXw@mail.gmail.com>

Hi Fuad,

On Tue, Feb 1, 2022 at 6:14 AM Fuad Tabba <tabba@google.com> wrote:
>
> Hi Reiji,
>
> ...
>
> > > > diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
> > > > index 0a06d0648970..28d9bf0e178c 100644
> > > > --- a/arch/arm64/kvm/vgic/vgic-init.c
> > > > +++ b/arch/arm64/kvm/vgic/vgic-init.c
> > > > @@ -116,6 +116,11 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
> > > >         else
> > > >                 INIT_LIST_HEAD(&kvm->arch.vgic.rd_regions);
> > > >
> > > > +       if (type == KVM_DEV_TYPE_ARM_VGIC_V3)
> > > > +               /* Set ID_AA64PFR0_EL1.GIC to 1 */
> > > > +               (void)kvm_set_id_reg_feature(kvm, SYS_ID_AA64PFR0_EL1,
> > > > +                                    ID_AA64PFR0_GIC3, ID_AA64PFR0_GIC_SHIFT);
> > > > +
> > >
> > > If this fails wouldn't it be better to return the error?
> >
> > This should never fail because kvm_vgic_create() prevents
> > userspace from running the first KVM_RUN for any vCPUs
> > while it calls kvm_set_id_reg_feature().
> > So, I am thinking of adding WARN_ON_ONCE() for the return value
> > rather than adding an unnecessary error handling.
>
> Consider this to be a nit from my part, as I don't have any strong
> feelings about this, but kvm_vgic_create() already returns an error if
> there's a problem. So I don't think that that would be imposing any
> additional error handling.

That's true.  But, since this failure case cannot be caused by userspace
(but KVM's bug), I would still prefer using WARN_ON_ONCE.

Thanks,
Reiji

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  reply	other threads:[~2022-02-10  5:35 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-06  4:26 [RFC PATCH v4 00/26] KVM: arm64: Make CPU ID registers writable by userspace Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 01/26] KVM: arm64: Introduce a validation function for an ID register Reiji Watanabe
2022-01-07  7:12   ` Reiji Watanabe
2022-01-24 16:20   ` Fuad Tabba
2022-01-26  6:04     ` Reiji Watanabe
2022-02-01 14:13       ` Fuad Tabba
2022-02-02  6:46         ` Reiji Watanabe
2022-01-26  4:30   ` Ricardo Koller
2022-01-28  6:01     ` Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 02/26] KVM: arm64: Save ID registers' sanitized value per guest Reiji Watanabe
2022-01-24 16:21   ` Fuad Tabba
2022-02-09  2:26     ` Reiji Watanabe
2022-01-26  5:22   ` Ricardo Koller
2022-01-28  6:24     ` Reiji Watanabe
2022-01-28 19:27       ` Ricardo Koller
2022-01-29  5:52         ` Reiji Watanabe
2022-01-31  3:40           ` Ricardo Koller
2022-02-01  6:00             ` Reiji Watanabe
2022-02-01 18:38               ` Ricardo Koller
2022-02-03  6:31                 ` Reiji Watanabe
2022-02-04 14:41                   ` Ricardo Koller
2022-01-06  4:26 ` [RFC PATCH v4 03/26] KVM: arm64: Introduce struct id_reg_info Reiji Watanabe
2022-01-24 16:28   ` Fuad Tabba
2022-01-26  6:46     ` Reiji Watanabe
2022-02-01 14:13       ` Fuad Tabba
2022-01-06  4:26 ` [RFC PATCH v4 04/26] KVM: arm64: Make ID_AA64PFR0_EL1 writable Reiji Watanabe
2022-01-24 16:51   ` Fuad Tabba
2022-01-27  4:01     ` Reiji Watanabe
2022-02-01 14:14       ` Fuad Tabba
2022-02-10  5:33         ` Reiji Watanabe [this message]
2022-01-06  4:26 ` [RFC PATCH v4 05/26] KVM: arm64: Make ID_AA64PFR1_EL1 writable Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 06/26] KVM: arm64: Make ID_AA64ISAR0_EL1 writable Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 07/26] KVM: arm64: Make ID_AA64ISAR1_EL1 writable Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 08/26] KVM: arm64: Make ID_AA64MMFR0_EL1 writable Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 09/26] KVM: arm64: Hide IMPLEMENTATION DEFINED PMU support for the guest Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 10/26] KVM: arm64: Make ID_AA64DFR0_EL1 writable Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 11/26] KVM: arm64: Make ID_DFR0_EL1 writable Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 12/26] KVM: arm64: Make MVFR1_EL1 writable Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 13/26] KVM: arm64: Make ID registers without id_reg_info writable Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 14/26] KVM: arm64: Add consistency checking for frac fields of ID registers Reiji Watanabe
2022-01-24 17:00   ` Fuad Tabba
2022-01-27  5:03     ` Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 15/26] KVM: arm64: Introduce KVM_CAP_ARM_ID_REG_CONFIGURABLE capability Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 16/26] KVM: arm64: Add kunit test for ID register validation Reiji Watanabe
2022-01-06  4:26 ` [RFC PATCH v4 17/26] KVM: arm64: Use vcpu->arch cptr_el2 to track value of cptr_el2 for VHE Reiji Watanabe
2022-01-06  4:27 ` [RFC PATCH v4 18/26] KVM: arm64: Use vcpu->arch.mdcr_el2 to track value of mdcr_el2 Reiji Watanabe
2022-01-06  4:27 ` [RFC PATCH v4 19/26] KVM: arm64: Introduce framework to trap disabled features Reiji Watanabe
2022-01-06  4:27 ` [RFC PATCH v4 20/26] KVM: arm64: Trap disabled features of ID_AA64PFR0_EL1 Reiji Watanabe
2022-01-24 17:16   ` Fuad Tabba
2022-01-27  7:19     ` Reiji Watanabe
2022-02-01 14:14       ` Fuad Tabba
2022-02-10  4:15         ` Reiji Watanabe
2022-01-06  4:27 ` [RFC PATCH v4 21/26] KVM: arm64: Trap disabled features of ID_AA64PFR1_EL1 Reiji Watanabe
2022-01-06  4:27 ` [RFC PATCH v4 22/26] KVM: arm64: Trap disabled features of ID_AA64DFR0_EL1 Reiji Watanabe
2022-01-24 17:19   ` Fuad Tabba
2022-01-28  5:40     ` Reiji Watanabe
2022-01-06  4:27 ` [RFC PATCH v4 23/26] KVM: arm64: Trap disabled features of ID_AA64MMFR1_EL1 Reiji Watanabe
2022-01-24 17:37   ` Fuad Tabba
2022-01-28  5:43     ` Reiji Watanabe
2022-02-09  4:51       ` Reiji Watanabe
2022-01-06  4:27 ` [RFC PATCH v4 24/26] KVM: arm64: Trap disabled features of ID_AA64ISAR1_EL1 Reiji Watanabe
2022-01-06  4:27 ` [RFC PATCH v4 25/26] KVM: arm64: Add kunit test for trap initialization Reiji Watanabe
2022-01-06  4:27 ` [RFC PATCH v4 26/26] KVM: arm64: selftests: Introduce id_reg_test Reiji Watanabe
2022-01-18  4:24 ` [RFC PATCH v4 00/26] KVM: arm64: Make CPU ID registers writable by userspace Reiji Watanabe
2022-01-24 16:18 ` Fuad Tabba
2022-01-25  6:31   ` Reiji Watanabe
2022-02-01 14:12     ` Fuad Tabba

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