linux-kernel - Re: [PATCH v4 2/7] arm64: KVM: Use shared area to pass PMU event state to hypervisor

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Date: Mon, 5 Feb 2024 13:21:26 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: Marc Zyngier <maz@...nel.org>
Cc: James Clark <james.clark@....com>, coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	broonie@...nel.org, suzuki.poulose@....com, acme@...nel.org,
	James Morse <james.morse@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Mike Leach <mike.leach@...aro.org>,
	Leo Yan <leo.yan@...aro.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Rob Herring <robh@...nel.org>, Miguel Luis <miguel.luis@...cle.com>,
	Jintack Lim <jintack.lim@...aro.org>,
	Ard Biesheuvel <ardb@...nel.org>,
	Mark Rutland <mark.rutland@....com>, Arnd Bergmann <arnd@...db.de>,
	Vincent Donnefort <vdonnefort@...gle.com>,
	Kristina Martsenko <kristina.martsenko@....com>,
	Fuad Tabba <tabba@...gle.com>, Joey Gouly <joey.gouly@....com>,
	Akihiko Odaki <akihiko.odaki@...nix.com>,
	Jing Zhang <jingzhangos@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/7] arm64: KVM: Use shared area to pass PMU event
 state to hypervisor

On Mon, Feb 05, 2024 at 01:15:36PM +0000, Marc Zyngier wrote:
> On Mon, 05 Feb 2024 13:04:51 +0000,
> Oliver Upton <oliver.upton@...ux.dev> wrote:
> > 
> > Unless someone has strong opinions about making this work in protected
> > mode, I am happy to see tracing support limited to the 'normal' nVHE
> > configuration. The protected feature as a whole is just baggage until
> > upstream support is completed.
> 
> Limiting tracing to non-protected mode is a must IMO. Allowing tracing
> when pKVM is enabled is a sure way to expose secrets that should
> stay... secret. The only exception I can think of is when
> CONFIG_NVHE_EL2_DEBUG is enabled, at which point all bets are off.

Zero argument there :) I left off the "and PMU" part of what I was
saying, because that was a feature that semi-worked in protected mode
before VM/VCPU shadowing support landed.

-- 
Thanks,
Oliver