linux-kernel - Re: [PATCH v4 0/4] KVM: arm64: Fix underallocation of storage for SVE state

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Message-ID: <86a5iw3ri2.wl-maz@kernel.org>
Date: Fri, 05 Jul 2024 14:20:05 +0100
From: Marc Zyngier <maz@...nel.org>
To: Mark Brown <broonie@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Fuad Tabba <tabba@...gle.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	kvmarm@...ts.linux.dev
Subject: Re: [PATCH v4 0/4] KVM: arm64: Fix underallocation of storage for SVE state

On Thu, 04 Jul 2024 18:28:15 +0100,
Mark Brown <broonie@...nel.org> wrote:
> 
> As observed during review the pKVM support for saving host SVE state is
> broken if an asymmetric system has VLs larger than the maximum shared
> VL, fix this by discovering then using the maximum VL for allocations
> and using RDVL during the save/restore process.

I really don't see why we need such complexity here.

Fuad did post something[1] that did the trick with a far less invasive
change, and it really feels like we are putting the complexity at the
wrong place.

So what's wrong with that approach? I get that you want to shout about
secondary CPUs, but that's an orthogonal problem.

	M.

[1] https://lore.kernel.org/r/20240606092623.2236172-1-tabba@google.com

-- 
Without deviation from the norm, progress is not possible.