From: Oliver Upton <oupton@google.com>
To: Reiji Watanabe <reijiw@google.com>
Cc: kvm@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
Peter Shier <pshier@google.com>, Will Deacon <will@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
kvmarm@lists.cs.columbia.edu,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v5 10/27] KVM: arm64: Hide IMPLEMENTATION DEFINED PMU support for the guest
Date: Thu, 17 Feb 2022 04:59:43 +0000 [thread overview]
Message-ID: <Yg3WP5HR9OJJMLj7@google.com> (raw)
In-Reply-To: <CAAeT=Fxvsniq4NW92LESqJ1ie6e+N1J793JrX0UBf2mq9B35dg@mail.gmail.com>
On Tue, Feb 15, 2022 at 06:52:27PM -0800, Reiji Watanabe wrote:
> Hi Oliver,
>
> Thank you for the review!
>
> On Tue, Feb 15, 2022 at 10:57 AM Oliver Upton <oupton@google.com> wrote:
> >
> > Hi Reiji,
> >
> > On Sun, Feb 13, 2022 at 10:57:29PM -0800, Reiji Watanabe wrote:
> > > When ID_AA64DFR0_EL1.PMUVER or ID_DFR0_EL1.PERFMON is 0xf, which
> > > means IMPLEMENTATION DEFINED PMU supported, KVM unconditionally
> > > expose the value for the guest as it is. Since KVM doesn't support
> > > IMPLEMENTATION DEFINED PMU for the guest, in that case KVM should
> > > expose 0x0 (PMU is not implemented) instead.
> > >
> > > Change cpuid_feature_cap_perfmon_field() to update the field value
> > > to 0x0 when it is 0xf.
> >
> > Definitely agree with the change in this patch. Do we need to tolerate
> > writes of 0xf for ABI compatibility (even if it is nonsensical)?
> > Otherwise a guest with IMP_DEF PMU cannot be migrated to a newer kernel.
>
> Hmm, yes, I think KVM should tolerate writes of 0xf so that we can
> avoid the migration failure. I will make this change in v6.
>
> Since ID registers are immutable with the current KVM, I think a live
> migration failure to a newer kernel happens when the newer kernel/KVM
> supports more CPU features (or when an ID register field is newly
> masked or capped by KVM, etc). So, I would assume such migration
> breakage on KVM/ARM has been introduced from time to time though.
>
Indeed it has, but IMO migration breakage should really be avoided at
all costs. End of the day, its ABI breakage.
Unless folks feel otherwise, I would be in favor of just ignoring the
IMP_DEF write and setting the field value to NI instead. Allows VMs to
migrate onto newer kernels and fixes the KVM bug at the same time.
--
Oliver
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
WARNING: multiple messages have this Message-ID (diff)
From: Oliver Upton <oupton@google.com>
To: Reiji Watanabe <reijiw@google.com>
Cc: Marc Zyngier <maz@kernel.org>,
kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Will Deacon <will@kernel.org>, Andrew Jones <drjones@redhat.com>,
Fuad Tabba <tabba@google.com>,
Peng Liang <liangpeng10@huawei.com>,
Peter Shier <pshier@google.com>,
Ricardo Koller <ricarkol@google.com>,
Jing Zhang <jingzhangos@google.com>,
Raghavendra Rao Anata <rananta@google.com>
Subject: Re: [PATCH v5 10/27] KVM: arm64: Hide IMPLEMENTATION DEFINED PMU support for the guest
Date: Thu, 17 Feb 2022 04:59:43 +0000 [thread overview]
Message-ID: <Yg3WP5HR9OJJMLj7@google.com> (raw)
In-Reply-To: <CAAeT=Fxvsniq4NW92LESqJ1ie6e+N1J793JrX0UBf2mq9B35dg@mail.gmail.com>
On Tue, Feb 15, 2022 at 06:52:27PM -0800, Reiji Watanabe wrote:
> Hi Oliver,
>
> Thank you for the review!
>
> On Tue, Feb 15, 2022 at 10:57 AM Oliver Upton <oupton@google.com> wrote:
> >
> > Hi Reiji,
> >
> > On Sun, Feb 13, 2022 at 10:57:29PM -0800, Reiji Watanabe wrote:
> > > When ID_AA64DFR0_EL1.PMUVER or ID_DFR0_EL1.PERFMON is 0xf, which
> > > means IMPLEMENTATION DEFINED PMU supported, KVM unconditionally
> > > expose the value for the guest as it is. Since KVM doesn't support
> > > IMPLEMENTATION DEFINED PMU for the guest, in that case KVM should
> > > expose 0x0 (PMU is not implemented) instead.
> > >
> > > Change cpuid_feature_cap_perfmon_field() to update the field value
> > > to 0x0 when it is 0xf.
> >
> > Definitely agree with the change in this patch. Do we need to tolerate
> > writes of 0xf for ABI compatibility (even if it is nonsensical)?
> > Otherwise a guest with IMP_DEF PMU cannot be migrated to a newer kernel.
>
> Hmm, yes, I think KVM should tolerate writes of 0xf so that we can
> avoid the migration failure. I will make this change in v6.
>
> Since ID registers are immutable with the current KVM, I think a live
> migration failure to a newer kernel happens when the newer kernel/KVM
> supports more CPU features (or when an ID register field is newly
> masked or capped by KVM, etc). So, I would assume such migration
> breakage on KVM/ARM has been introduced from time to time though.
>
Indeed it has, but IMO migration breakage should really be avoided at
all costs. End of the day, its ABI breakage.
Unless folks feel otherwise, I would be in favor of just ignoring the
IMP_DEF write and setting the field value to NI instead. Allows VMs to
migrate onto newer kernels and fixes the KVM bug at the same time.
--
Oliver
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
WARNING: multiple messages have this Message-ID (diff)
From: Oliver Upton <oupton@google.com>
To: Reiji Watanabe <reijiw@google.com>
Cc: Marc Zyngier <maz@kernel.org>,
kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Will Deacon <will@kernel.org>, Andrew Jones <drjones@redhat.com>,
Fuad Tabba <tabba@google.com>,
Peng Liang <liangpeng10@huawei.com>,
Peter Shier <pshier@google.com>,
Ricardo Koller <ricarkol@google.com>,
Jing Zhang <jingzhangos@google.com>,
Raghavendra Rao Anata <rananta@google.com>
Subject: Re: [PATCH v5 10/27] KVM: arm64: Hide IMPLEMENTATION DEFINED PMU support for the guest
Date: Thu, 17 Feb 2022 04:59:43 +0000 [thread overview]
Message-ID: <Yg3WP5HR9OJJMLj7@google.com> (raw)
In-Reply-To: <CAAeT=Fxvsniq4NW92LESqJ1ie6e+N1J793JrX0UBf2mq9B35dg@mail.gmail.com>
On Tue, Feb 15, 2022 at 06:52:27PM -0800, Reiji Watanabe wrote:
> Hi Oliver,
>
> Thank you for the review!
>
> On Tue, Feb 15, 2022 at 10:57 AM Oliver Upton <oupton@google.com> wrote:
> >
> > Hi Reiji,
> >
> > On Sun, Feb 13, 2022 at 10:57:29PM -0800, Reiji Watanabe wrote:
> > > When ID_AA64DFR0_EL1.PMUVER or ID_DFR0_EL1.PERFMON is 0xf, which
> > > means IMPLEMENTATION DEFINED PMU supported, KVM unconditionally
> > > expose the value for the guest as it is. Since KVM doesn't support
> > > IMPLEMENTATION DEFINED PMU for the guest, in that case KVM should
> > > expose 0x0 (PMU is not implemented) instead.
> > >
> > > Change cpuid_feature_cap_perfmon_field() to update the field value
> > > to 0x0 when it is 0xf.
> >
> > Definitely agree with the change in this patch. Do we need to tolerate
> > writes of 0xf for ABI compatibility (even if it is nonsensical)?
> > Otherwise a guest with IMP_DEF PMU cannot be migrated to a newer kernel.
>
> Hmm, yes, I think KVM should tolerate writes of 0xf so that we can
> avoid the migration failure. I will make this change in v6.
>
> Since ID registers are immutable with the current KVM, I think a live
> migration failure to a newer kernel happens when the newer kernel/KVM
> supports more CPU features (or when an ID register field is newly
> masked or capped by KVM, etc). So, I would assume such migration
> breakage on KVM/ARM has been introduced from time to time though.
>
Indeed it has, but IMO migration breakage should really be avoided at
all costs. End of the day, its ABI breakage.
Unless folks feel otherwise, I would be in favor of just ignoring the
IMP_DEF write and setting the field value to NI instead. Allows VMs to
migrate onto newer kernels and fixes the KVM bug at the same time.
--
Oliver
next prev parent reply other threads:[~2022-02-17 4:59 UTC|newest]
Thread overview: 105+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-14 6:57 [PATCH v5 00/27] KVM: arm64: Make CPU ID registers writable by userspace Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 01/27] KVM: arm64: Introduce a validation function for an ID register Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 02/27] KVM: arm64: Save ID registers' sanitized value per guest Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 03/27] KVM: arm64: Introduce struct id_reg_info Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-17 5:14 ` Oliver Upton
2022-02-17 5:14 ` Oliver Upton
2022-02-17 5:14 ` Oliver Upton
2022-02-22 6:12 ` Reiji Watanabe
2022-02-22 6:12 ` Reiji Watanabe
2022-02-22 6:12 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 04/27] KVM: arm64: Make ID_AA64PFR0_EL1 writable Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 05/27] KVM: arm64: Make ID_AA64PFR1_EL1 writable Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 06/27] KVM: arm64: Make ID_AA64ISAR0_EL1 writable Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 07/27] KVM: arm64: Make ID_AA64ISAR1_EL1 writable Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 08/27] KVM: arm64: Make ID_AA64MMFR0_EL1 writable Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 09/27] KVM: arm64: Make ID_AA64MMFR1_EL1 writable Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-15 18:53 ` Oliver Upton
2022-02-15 18:53 ` Oliver Upton
2022-02-15 18:53 ` Oliver Upton
2022-02-15 20:24 ` Reiji Watanabe
2022-02-15 20:24 ` Reiji Watanabe
2022-02-15 20:24 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 10/27] KVM: arm64: Hide IMPLEMENTATION DEFINED PMU support for the guest Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-15 18:57 ` Oliver Upton
2022-02-15 18:57 ` Oliver Upton
2022-02-15 18:57 ` Oliver Upton
2022-02-16 2:52 ` Reiji Watanabe
2022-02-16 2:52 ` Reiji Watanabe
2022-02-16 2:52 ` Reiji Watanabe
2022-02-17 4:59 ` Oliver Upton [this message]
2022-02-17 4:59 ` Oliver Upton
2022-02-17 4:59 ` Oliver Upton
2022-02-14 6:57 ` [PATCH v5 11/27] KVM: arm64: Make ID_AA64DFR0_EL1 writable Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 12/27] KVM: arm64: Make ID_DFR0_EL1 writable Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 13/27] KVM: arm64: Make MVFR1_EL1 writable Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 14/27] KVM: arm64: Make ID registers without id_reg_info writable Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 15/27] KVM: arm64: Add consistency checking for frac fields of ID registers Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 16/27] KVM: arm64: Introduce KVM_CAP_ARM_ID_REG_CONFIGURABLE capability Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 17/27] KVM: arm64: Add kunit test for ID register validation Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 18/27] KVM: arm64: Use vcpu->arch cptr_el2 to track value of cptr_el2 for VHE Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 19/27] KVM: arm64: Use vcpu->arch.mdcr_el2 to track value of mdcr_el2 Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 20/27] KVM: arm64: Introduce framework to trap disabled features Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 21/27] KVM: arm64: Trap disabled features of ID_AA64PFR0_EL1 Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 22/27] KVM: arm64: Trap disabled features of ID_AA64PFR1_EL1 Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 23/27] KVM: arm64: Trap disabled features of ID_AA64DFR0_EL1 Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 24/27] KVM: arm64: Trap disabled features of ID_AA64MMFR1_EL1 Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 25/27] KVM: arm64: Trap disabled features of ID_AA64ISAR1_EL1 Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 26/27] KVM: arm64: Add kunit test for trap initialization Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` [PATCH v5 27/27] KVM: arm64: selftests: Introduce id_reg_test Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
2022-02-14 6:57 ` Reiji Watanabe
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