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From: Oliver Upton <oliver.upton@linux.dev>
To: Marc Zyngier <maz@kernel.org>
Cc: Akihiko Odaki <akihiko.odaki@daynix.com>,
	linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	James Morse <james.morse@arm.com>, Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	asahi@lists.linux.dev, Alyssa Rosenzweig <alyssa@rosenzweig.io>,
	Sven Peter <sven@svenpeter.dev>, Hector Martin <marcan@marcan.st>
Subject: Re: [PATCH 0/3] KVM: arm64: Handle CCSIDR associativity mismatches
Date: Thu, 1 Dec 2022 18:29:51 +0000	[thread overview]
Message-ID: <Y4jyn+aMUGcaa6Ag@google.com> (raw)
In-Reply-To: <867czbmlh1.wl-maz@kernel.org>

On Thu, Dec 01, 2022 at 11:06:50AM +0000, Marc Zyngier wrote:

[...]

> It would be a lot better to expose a virtual topology
> (one set, one way, one level). It would also save us from the CCSIDRX
> silliness.
> 
> The only complexity would be to still accept different topologies from
> userspace so that we can restore a VM saved before this virtual
> topology.

I generally agree that the reported topology is meaningless to
non-secure software.

However, with the cloud vendor hat on, I'm worried that inevitably some
customer will inspect the cache topology of the VM we've provided them
and complain.

Could we extend your suggestion about accepting different topologies to
effectively tolerate _any_ topology provided by userspace? KVM can
default to the virtual topology, but a well-informed userspace could
still provide different values to its guest. No point in trying to
babyproofing the UAPI further, IMO.

--
Thanks,
Oliver

WARNING: multiple messages have this Message-ID (diff)
From: Oliver Upton <oliver.upton@linux.dev>
To: Marc Zyngier <maz@kernel.org>
Cc: Alyssa Rosenzweig <alyssa@rosenzweig.io>,
	Hector Martin <marcan@marcan.st>,
	Akihiko Odaki <akihiko.odaki@daynix.com>,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	Will Deacon <will@kernel.org>, Sven Peter <sven@svenpeter.dev>,
	linux-kernel@vger.kernel.org, asahi@lists.linux.dev,
	Catalin Marinas <catalin.marinas@arm.com>,
	kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 0/3] KVM: arm64: Handle CCSIDR associativity mismatches
Date: Thu, 1 Dec 2022 18:29:51 +0000	[thread overview]
Message-ID: <Y4jyn+aMUGcaa6Ag@google.com> (raw)
In-Reply-To: <867czbmlh1.wl-maz@kernel.org>

On Thu, Dec 01, 2022 at 11:06:50AM +0000, Marc Zyngier wrote:

[...]

> It would be a lot better to expose a virtual topology
> (one set, one way, one level). It would also save us from the CCSIDRX
> silliness.
> 
> The only complexity would be to still accept different topologies from
> userspace so that we can restore a VM saved before this virtual
> topology.

I generally agree that the reported topology is meaningless to
non-secure software.

However, with the cloud vendor hat on, I'm worried that inevitably some
customer will inspect the cache topology of the VM we've provided them
and complain.

Could we extend your suggestion about accepting different topologies to
effectively tolerate _any_ topology provided by userspace? KVM can
default to the virtual topology, but a well-informed userspace could
still provide different values to its guest. No point in trying to
babyproofing the UAPI further, IMO.

--
Thanks,
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 <oliver.upton@linux.dev>
To: Marc Zyngier <maz@kernel.org>
Cc: Akihiko Odaki <akihiko.odaki@daynix.com>,
	linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	James Morse <james.morse@arm.com>, Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	asahi@lists.linux.dev, Alyssa Rosenzweig <alyssa@rosenzweig.io>,
	Sven Peter <sven@svenpeter.dev>, Hector Martin <marcan@marcan.st>
Subject: Re: [PATCH 0/3] KVM: arm64: Handle CCSIDR associativity mismatches
Date: Thu, 1 Dec 2022 18:29:51 +0000	[thread overview]
Message-ID: <Y4jyn+aMUGcaa6Ag@google.com> (raw)
In-Reply-To: <867czbmlh1.wl-maz@kernel.org>

On Thu, Dec 01, 2022 at 11:06:50AM +0000, Marc Zyngier wrote:

[...]

> It would be a lot better to expose a virtual topology
> (one set, one way, one level). It would also save us from the CCSIDRX
> silliness.
> 
> The only complexity would be to still accept different topologies from
> userspace so that we can restore a VM saved before this virtual
> topology.

I generally agree that the reported topology is meaningless to
non-secure software.

However, with the cloud vendor hat on, I'm worried that inevitably some
customer will inspect the cache topology of the VM we've provided them
and complain.

Could we extend your suggestion about accepting different topologies to
effectively tolerate _any_ topology provided by userspace? KVM can
default to the virtual topology, but a well-informed userspace could
still provide different values to its guest. No point in trying to
babyproofing the UAPI further, IMO.

--
Thanks,
Oliver

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

  parent reply	other threads:[~2022-12-01 18:30 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-01 10:49 [PATCH 0/3] KVM: arm64: Handle CCSIDR associativity mismatches Akihiko Odaki
2022-12-01 10:49 ` Akihiko Odaki
2022-12-01 10:49 ` Akihiko Odaki
2022-12-01 10:49 ` Akihiko Odaki
2022-12-01 10:49 ` [PATCH 1/3] KVM: arm64: Make CCSIDRs consistent Akihiko Odaki
2022-12-01 10:49   ` Akihiko Odaki
2022-12-01 10:49   ` Akihiko Odaki
2022-12-01 10:49   ` Akihiko Odaki
2022-12-01 10:49 ` [PATCH 2/3] arm64: errata: Check for mismatched cache associativity Akihiko Odaki
2022-12-01 10:49   ` Akihiko Odaki
2022-12-01 10:49   ` Akihiko Odaki
2022-12-01 10:49   ` Akihiko Odaki
2022-12-01 10:49 ` [PATCH 3/3] KVM: arm64: Handle CCSIDR associativity mismatches Akihiko Odaki
2022-12-01 10:49   ` Akihiko Odaki
2022-12-01 10:49   ` Akihiko Odaki
2022-12-01 10:49   ` Akihiko Odaki
2022-12-01 11:06 ` [PATCH 0/3] " Marc Zyngier
2022-12-01 11:06   ` Marc Zyngier
2022-12-01 11:06   ` Marc Zyngier
2022-12-01 17:26   ` Akihiko Odaki
2022-12-01 17:26     ` Akihiko Odaki
2022-12-01 17:26     ` Akihiko Odaki
2022-12-01 23:13     ` Marc Zyngier
2022-12-01 23:13       ` Marc Zyngier
2022-12-01 23:13       ` Marc Zyngier
2022-12-02  5:17       ` Akihiko Odaki
2022-12-02  5:17         ` Akihiko Odaki
2022-12-02  5:17         ` Akihiko Odaki
2022-12-02  9:40         ` Marc Zyngier
2022-12-02  9:40           ` Marc Zyngier
2022-12-02  9:40           ` Marc Zyngier
2022-12-02  9:55           ` Akihiko Odaki
2022-12-02  9:55             ` Akihiko Odaki
2022-12-02  9:55             ` Akihiko Odaki
2022-12-04 14:57             ` Marc Zyngier
2022-12-04 14:57               ` Marc Zyngier
2022-12-04 14:57               ` Marc Zyngier
2022-12-11  5:25               ` Akihiko Odaki
2022-12-11  5:25                 ` Akihiko Odaki
2022-12-11  5:25                 ` Akihiko Odaki
2022-12-11 10:21                 ` Marc Zyngier
2022-12-11 10:21                   ` Marc Zyngier
2022-12-11 10:21                   ` Marc Zyngier
2022-12-11 10:44                   ` Akihiko Odaki
2022-12-11 10:44                     ` Akihiko Odaki
2022-12-11 10:44                     ` Akihiko Odaki
2022-12-01 18:29   ` Oliver Upton [this message]
2022-12-01 18:29     ` Oliver Upton
2022-12-01 18:29     ` Oliver Upton
2022-12-01 23:14     ` Marc Zyngier
2022-12-01 23:14       ` Marc Zyngier
2022-12-01 23:14       ` Marc Zyngier
2022-12-02 18:54       ` Oliver Upton
2022-12-02 18:54         ` Oliver Upton
2022-12-02 18:54         ` Oliver Upton

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