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From: Andrew Jones <drjones@redhat.com>
To: Will Deacon <will@kernel.org>
Cc: Fuad Tabba <tabba@google.com>,
	kvmarm@lists.cs.columbia.edu, maz@kernel.org,
	james.morse@arm.com, alexandru.elisei@arm.com,
	suzuki.poulose@arm.com, mark.rutland@arm.com,
	christoffer.dall@arm.com, pbonzini@redhat.com,
	qperret@google.com, kvm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, kernel-team@android.com
Subject: Re: [PATCH v2 09/13] KVM: arm64: Add trap handlers for protected VMs
Date: Wed, 14 Jul 2021 22:01:48 +0200	[thread overview]
Message-ID: <20210714200148.vjujrwsn2qsfd6kd@gator> (raw)
In-Reply-To: <20210701140821.GI9757@willie-the-truck>

On Thu, Jul 01, 2021 at 03:08:22PM +0100, Will Deacon wrote:
> On Tue, Jun 15, 2021 at 02:39:46PM +0100, Fuad Tabba wrote:
> > Add trap handlers for protected VMs. These are mainly for Sys64
> > and debug traps.
> 
> I think one big thing missing from this patch is some rationale around
> which features are advertised and which are not. Further, when traps
> are enabled later on, there doesn't seem to be one place which drives the
> logic, so it's quite hard to reason about.
> 
> So I think we need both some documentation to describe the architectural
> environment provided to protected VMs, but also a way to couple the logic
> which says "We hide this feature from the ID registers because of foo"
> with the logic that says "And here is the control bit to trap this feature".

I think it would be better to have documentation that says "We expose this
feature because foo". If the feature doesn't have any rationale to be
exposed, then it's just not. It may also make sense to document features
that should never be exposed, if there are features like that, in order to
ensure nobody comes along and exposes them later.

Thanks,
drew


WARNING: multiple messages have this Message-ID (diff)
From: Andrew Jones <drjones@redhat.com>
To: Will Deacon <will@kernel.org>
Cc: kernel-team@android.com, kvm@vger.kernel.org, maz@kernel.org,
	linux-arm-kernel@lists.infradead.org, pbonzini@redhat.com,
	kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v2 09/13] KVM: arm64: Add trap handlers for protected VMs
Date: Wed, 14 Jul 2021 22:01:48 +0200	[thread overview]
Message-ID: <20210714200148.vjujrwsn2qsfd6kd@gator> (raw)
In-Reply-To: <20210701140821.GI9757@willie-the-truck>

On Thu, Jul 01, 2021 at 03:08:22PM +0100, Will Deacon wrote:
> On Tue, Jun 15, 2021 at 02:39:46PM +0100, Fuad Tabba wrote:
> > Add trap handlers for protected VMs. These are mainly for Sys64
> > and debug traps.
> 
> I think one big thing missing from this patch is some rationale around
> which features are advertised and which are not. Further, when traps
> are enabled later on, there doesn't seem to be one place which drives the
> logic, so it's quite hard to reason about.
> 
> So I think we need both some documentation to describe the architectural
> environment provided to protected VMs, but also a way to couple the logic
> which says "We hide this feature from the ID registers because of foo"
> with the logic that says "And here is the control bit to trap this feature".

I think it would be better to have documentation that says "We expose this
feature because foo". If the feature doesn't have any rationale to be
exposed, then it's just not. It may also make sense to document features
that should never be exposed, if there are features like that, in order to
ensure nobody comes along and exposes them later.

Thanks,
drew

_______________________________________________
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: Andrew Jones <drjones@redhat.com>
To: Will Deacon <will@kernel.org>
Cc: Fuad Tabba <tabba@google.com>,
	kvmarm@lists.cs.columbia.edu, maz@kernel.org,
	james.morse@arm.com, alexandru.elisei@arm.com,
	suzuki.poulose@arm.com, mark.rutland@arm.com,
	christoffer.dall@arm.com, pbonzini@redhat.com,
	qperret@google.com, kvm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, kernel-team@android.com
Subject: Re: [PATCH v2 09/13] KVM: arm64: Add trap handlers for protected VMs
Date: Wed, 14 Jul 2021 22:01:48 +0200	[thread overview]
Message-ID: <20210714200148.vjujrwsn2qsfd6kd@gator> (raw)
In-Reply-To: <20210701140821.GI9757@willie-the-truck>

On Thu, Jul 01, 2021 at 03:08:22PM +0100, Will Deacon wrote:
> On Tue, Jun 15, 2021 at 02:39:46PM +0100, Fuad Tabba wrote:
> > Add trap handlers for protected VMs. These are mainly for Sys64
> > and debug traps.
> 
> I think one big thing missing from this patch is some rationale around
> which features are advertised and which are not. Further, when traps
> are enabled later on, there doesn't seem to be one place which drives the
> logic, so it's quite hard to reason about.
> 
> So I think we need both some documentation to describe the architectural
> environment provided to protected VMs, but also a way to couple the logic
> which says "We hide this feature from the ID registers because of foo"
> with the logic that says "And here is the control bit to trap this feature".

I think it would be better to have documentation that says "We expose this
feature because foo". If the feature doesn't have any rationale to be
exposed, then it's just not. It may also make sense to document features
that should never be exposed, if there are features like that, in order to
ensure nobody comes along and exposes them later.

Thanks,
drew


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-07-14 20:02 UTC|newest]

Thread overview: 96+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-15 13:39 [PATCH v2 00/13] KVM: arm64: Fixed features for protected VMs Fuad Tabba
2021-06-15 13:39 ` Fuad Tabba
2021-06-15 13:39 ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 01/13] KVM: arm64: Remove trailing whitespace in comments Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-07-01 12:55   ` Will Deacon
2021-07-01 12:55     ` Will Deacon
2021-07-01 12:55     ` Will Deacon
2021-07-01 13:24     ` Fuad Tabba
2021-07-01 13:24       ` Fuad Tabba
2021-07-01 13:24       ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 02/13] KVM: arm64: MDCR_EL2 is a 64-bit register Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-07-01 12:53   ` Will Deacon
2021-07-01 12:53     ` Will Deacon
2021-07-01 12:53     ` Will Deacon
2021-07-01 13:24     ` Fuad Tabba
2021-07-01 13:24       ` Fuad Tabba
2021-07-01 13:24       ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 03/13] KVM: arm64: Fix names of config register fields Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-07-01 13:01   ` Will Deacon
2021-07-01 13:01     ` Will Deacon
2021-07-01 13:01     ` Will Deacon
2021-07-01 13:44     ` Fuad Tabba
2021-07-01 13:44       ` Fuad Tabba
2021-07-01 13:44       ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 04/13] KVM: arm64: Refactor sys_regs.h,c for nVHE reuse Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-07-01 13:09   ` Will Deacon
2021-07-01 13:09     ` [PATCH v2 04/13] KVM: arm64: Refactor sys_regs.h, c " Will Deacon
2021-07-01 13:09     ` Will Deacon
2021-07-01 14:04     ` [PATCH v2 04/13] KVM: arm64: Refactor sys_regs.h,c " Fuad Tabba
2021-07-01 14:04       ` [PATCH v2 04/13] KVM: arm64: Refactor sys_regs.h, c " Fuad Tabba
2021-07-01 14:04       ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 05/13] KVM: arm64: Restore mdcr_el2 from vcpu Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-07-01 13:17   ` Will Deacon
2021-07-01 13:17     ` Will Deacon
2021-07-01 13:17     ` Will Deacon
2021-07-01 14:05     ` Fuad Tabba
2021-07-01 14:05       ` Fuad Tabba
2021-07-01 14:05       ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 06/13] KVM: arm64: Add feature register flag definitions Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-07-01 13:22   ` Will Deacon
2021-07-01 13:22     ` Will Deacon
2021-07-01 13:22     ` Will Deacon
2021-07-01 14:31     ` Fuad Tabba
2021-07-01 14:31       ` Fuad Tabba
2021-07-01 14:31       ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 07/13] KVM: arm64: Add config register bit definitions Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-07-01 13:33   ` Will Deacon
2021-07-01 13:33     ` Will Deacon
2021-07-01 13:33     ` Will Deacon
2021-07-01 14:52     ` Fuad Tabba
2021-07-01 14:52       ` Fuad Tabba
2021-07-01 14:52       ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 08/13] KVM: arm64: Guest exit handlers for nVHE hyp Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-07-01 13:48   ` Will Deacon
2021-07-01 13:48     ` Will Deacon
2021-07-01 13:48     ` Will Deacon
2021-07-01 14:58     ` Fuad Tabba
2021-07-01 14:58       ` Fuad Tabba
2021-07-01 14:58       ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 09/13] KVM: arm64: Add trap handlers for protected VMs Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-07-01 14:08   ` Will Deacon
2021-07-01 14:08     ` Will Deacon
2021-07-01 14:08     ` Will Deacon
2021-07-14 20:01     ` Andrew Jones [this message]
2021-07-14 20:01       ` Andrew Jones
2021-07-14 20:01       ` Andrew Jones
2021-06-15 13:39 ` [PATCH v2 10/13] KVM: arm64: Move sanitized copies of CPU features Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 11/13] KVM: arm64: Trap access to pVM restricted features Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 12/13] KVM: arm64: Handle protected guests at 32 bits Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39 ` [PATCH v2 13/13] KVM: arm64: Check vcpu features at pVM creation Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba
2021-06-15 13:39   ` Fuad Tabba

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