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

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Message-ID: <Ztspjf0SHx7nz2lV@finisterre.sirena.org.uk>
Date: Fri, 6 Sep 2024 17:10:53 +0100
From: Mark Brown <broonie@...nel.org>
To: Fuad Tabba <tabba@...gle.com>
Cc: Dave Martin <Dave.Martin@....com>, Marc Zyngier <maz@...nel.org>,
	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>,
	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 Fri, Sep 06, 2024 at 04:35:29PM +0100, Fuad Tabba wrote:

> > > Can't pKVM just hide the non symmetrically supported VLs using ZCR_EL2,
> > > just as regular KVM does for the guest?

> > > (I may be making bad assumptions about pKVM's relationship with the host
> > > kernel.)

> > That's one for the pKVM people.

> Yes, but that's not really the issue here, unless I'm missing
> something else. The issue is that pKVM needs to store the host's SVE
> state too, to be able to restore it. So hiding non-symmetrically
> supported VLs for the guests shouldn't be relevant.

If the host kernel is also running at EL1 and it's only the hypervisor
running at EL2 then the hypervisor can control the VLs that the host
kernel is able to access?

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