From: Catalin Marinas <catalin.marinas@arm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>, Will Deacon <will@kernel.org>,
Peter Maydell <peter.maydell@linaro.org>,
Richard Henderson <richard.henderson@linaro.org>,
Vincent Donnefort <vdonnefort@google.com>,
James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Oliver Upton <oliver.upton@linux.dev>,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev
Subject: Re: [PATCH v1 0/2] KVM: arm: Refuse to enable KVM on systems with SME but not FGT
Date: Sun, 30 Oct 2022 17:44:39 +0000 [thread overview]
Message-ID: <Y164B4m50JW6Y0hA@arm.com> (raw)
In-Reply-To: <8735b6hmxo.wl-maz@kernel.org>
On Sat, Oct 29, 2022 at 12:46:43PM +0100, Marc Zyngier wrote:
> On Thu, 27 Oct 2022 21:52:44 +0100,
> Mark Brown <broonie@kernel.org> wrote:
> >
> > The architecture requires that any system which implements SME also has
> > fine grained traps since SME is a v9.2 feature, meaning that v8.7 must be
> > implemented, and FGT is mandatory from v8.6. SME relies on fine grained
> > traps to control access to SMPRI_EL1 and in nVHE mode to TPIDR2_EL0,
> > without traps SMPRI_EL1.Priority and TPIDR2_EL0 can be used as side
> > channels.
> >
> > This series adds support for detecting FGT and refuses to allow KVM to
> > be used in architecturally invalid configurations which have SME but not
> > FGT, without detection the issue presents as faults due to EL2
> > attempting to access the FGT registers which isn't obvious to users.
> > Currently fine grained traps are only used in nVHE but but a series
> > "arm64/sme: Fix SMPRI_EL1 traps for KVM guests" sent along with this
> > will add usage for VHE mode too making the issue more pressing.
>
> I think this goes the wrong way around. SME without FGT is invalid,
> and yet you keep SME around and device to kill virtualisation support.
>
> I'd rather it is SME that gets disabled when the kernel boots at EL2.
I agree, I rather we did it the other way around.
--
Catalin
WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>, Will Deacon <will@kernel.org>,
Peter Maydell <peter.maydell@linaro.org>,
Richard Henderson <richard.henderson@linaro.org>,
Vincent Donnefort <vdonnefort@google.com>,
James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Oliver Upton <oliver.upton@linux.dev>,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev
Subject: Re: [PATCH v1 0/2] KVM: arm: Refuse to enable KVM on systems with SME but not FGT
Date: Sun, 30 Oct 2022 17:44:39 +0000 [thread overview]
Message-ID: <Y164B4m50JW6Y0hA@arm.com> (raw)
In-Reply-To: <8735b6hmxo.wl-maz@kernel.org>
On Sat, Oct 29, 2022 at 12:46:43PM +0100, Marc Zyngier wrote:
> On Thu, 27 Oct 2022 21:52:44 +0100,
> Mark Brown <broonie@kernel.org> wrote:
> >
> > The architecture requires that any system which implements SME also has
> > fine grained traps since SME is a v9.2 feature, meaning that v8.7 must be
> > implemented, and FGT is mandatory from v8.6. SME relies on fine grained
> > traps to control access to SMPRI_EL1 and in nVHE mode to TPIDR2_EL0,
> > without traps SMPRI_EL1.Priority and TPIDR2_EL0 can be used as side
> > channels.
> >
> > This series adds support for detecting FGT and refuses to allow KVM to
> > be used in architecturally invalid configurations which have SME but not
> > FGT, without detection the issue presents as faults due to EL2
> > attempting to access the FGT registers which isn't obvious to users.
> > Currently fine grained traps are only used in nVHE but but a series
> > "arm64/sme: Fix SMPRI_EL1 traps for KVM guests" sent along with this
> > will add usage for VHE mode too making the issue more pressing.
>
> I think this goes the wrong way around. SME without FGT is invalid,
> and yet you keep SME around and device to kill virtualisation support.
>
> I'd rather it is SME that gets disabled when the kernel boots at EL2.
I agree, I rather we did it the other way around.
--
Catalin
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next prev parent reply other threads:[~2022-10-30 17:44 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-27 20:52 [PATCH v1 0/2] KVM: arm: Refuse to enable KVM on systems with SME but not FGT Mark Brown
2022-10-27 20:52 ` Mark Brown
2022-10-27 20:52 ` [PATCH v1 1/2] arm64/cpufeature: Add feature detection for fine grained traps Mark Brown
2022-10-27 20:52 ` Mark Brown
2022-10-27 20:52 ` [PATCH v1 2/2] KVM: arm: Refuse to enable KVM on systems with FEAT_SME but not FEAT_FGT Mark Brown
2022-10-27 20:52 ` Mark Brown
2022-10-27 21:17 ` [PATCH v1 0/2] KVM: arm: Refuse to enable KVM on systems with SME but not FGT Richard Henderson
2022-10-27 21:17 ` Richard Henderson
2022-10-29 11:46 ` Marc Zyngier
2022-10-29 11:46 ` Marc Zyngier
2022-10-30 17:44 ` Catalin Marinas [this message]
2022-10-30 17:44 ` Catalin Marinas
2022-10-31 12:38 ` Mark Brown
2022-10-31 12:38 ` Mark Brown
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