From: Quentin Perret <qperret@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Andrew Scull <ascull@google.com>, Will Deacon <will@kernel.org>,
kernel-team@android.com
Subject: Re: [PATCH 1/8] KVM: arm64: Don't corrupt tpidr_el2 on failed HVC call
Date: Mon, 26 Oct 2020 14:36:23 +0000 [thread overview]
Message-ID: <20201026143623.GA2229434@google.com> (raw)
In-Reply-To: <20201026095116.72051-2-maz@kernel.org>
On Monday 26 Oct 2020 at 09:51:09 (+0000), Marc Zyngier wrote:
> The hyp-init code starts by stashing a register in TPIDR_EL2
> in in order to free a register. This happens no matter if the
> HVC call is legal or not.
>
> Although nothing wrong seems to come out of it, it feels odd
> to alter the EL2 state for something that eventually returns
> an error.
>
> Instead, use the fact that we know exactly which bits of the
> __kvm_hyp_init call are non-zero to perform the check with
> a series of EOR/ROR instructions, combined with a build-time
> check that the value is the one we expect.
Alternatively, could we make __kvm_hyp_init non-SMCCC compliant? While I
understand how it makes sense to be compliant for 'proper' HVCs, this
one really is an odd one that only makes sense on a very transient state.
That would let us define our convention, and we can just say x0-x18 can
be clobbered like any function call, which eradicates the issue Andrew
tried to avoid with this tpidr_el2 trick.
Thoughts?
Thanks,
Quentin
WARNING: multiple messages have this Message-ID (diff)
From: Quentin Perret <qperret@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: kvm@vger.kernel.org, kernel-team@android.com,
linux-arm-kernel@lists.infradead.org,
Will Deacon <will@kernel.org>,
kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH 1/8] KVM: arm64: Don't corrupt tpidr_el2 on failed HVC call
Date: Mon, 26 Oct 2020 14:36:23 +0000 [thread overview]
Message-ID: <20201026143623.GA2229434@google.com> (raw)
In-Reply-To: <20201026095116.72051-2-maz@kernel.org>
On Monday 26 Oct 2020 at 09:51:09 (+0000), Marc Zyngier wrote:
> The hyp-init code starts by stashing a register in TPIDR_EL2
> in in order to free a register. This happens no matter if the
> HVC call is legal or not.
>
> Although nothing wrong seems to come out of it, it feels odd
> to alter the EL2 state for something that eventually returns
> an error.
>
> Instead, use the fact that we know exactly which bits of the
> __kvm_hyp_init call are non-zero to perform the check with
> a series of EOR/ROR instructions, combined with a build-time
> check that the value is the one we expect.
Alternatively, could we make __kvm_hyp_init non-SMCCC compliant? While I
understand how it makes sense to be compliant for 'proper' HVCs, this
one really is an odd one that only makes sense on a very transient state.
That would let us define our convention, and we can just say x0-x18 can
be clobbered like any function call, which eradicates the issue Andrew
tried to avoid with this tpidr_el2 trick.
Thoughts?
Thanks,
Quentin
_______________________________________________
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: Quentin Perret <qperret@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: kvm@vger.kernel.org, Suzuki K Poulose <suzuki.poulose@arm.com>,
kernel-team@android.com, James Morse <james.morse@arm.com>,
linux-arm-kernel@lists.infradead.org,
Will Deacon <will@kernel.org>,
kvmarm@lists.cs.columbia.edu,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Andrew Scull <ascull@google.com>
Subject: Re: [PATCH 1/8] KVM: arm64: Don't corrupt tpidr_el2 on failed HVC call
Date: Mon, 26 Oct 2020 14:36:23 +0000 [thread overview]
Message-ID: <20201026143623.GA2229434@google.com> (raw)
In-Reply-To: <20201026095116.72051-2-maz@kernel.org>
On Monday 26 Oct 2020 at 09:51:09 (+0000), Marc Zyngier wrote:
> The hyp-init code starts by stashing a register in TPIDR_EL2
> in in order to free a register. This happens no matter if the
> HVC call is legal or not.
>
> Although nothing wrong seems to come out of it, it feels odd
> to alter the EL2 state for something that eventually returns
> an error.
>
> Instead, use the fact that we know exactly which bits of the
> __kvm_hyp_init call are non-zero to perform the check with
> a series of EOR/ROR instructions, combined with a build-time
> check that the value is the one we expect.
Alternatively, could we make __kvm_hyp_init non-SMCCC compliant? While I
understand how it makes sense to be compliant for 'proper' HVCs, this
one really is an odd one that only makes sense on a very transient state.
That would let us define our convention, and we can just say x0-x18 can
be clobbered like any function call, which eradicates the issue Andrew
tried to avoid with this tpidr_el2 trick.
Thoughts?
Thanks,
Quentin
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-10-26 14:40 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-26 9:51 [PATCH 0/8] KVM: arm64: Host EL2 entry improvements Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` [PATCH 1/8] KVM: arm64: Don't corrupt tpidr_el2 on failed HVC call Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 14:36 ` Quentin Perret [this message]
2020-10-26 14:36 ` Quentin Perret
2020-10-26 14:36 ` Quentin Perret
2020-10-26 9:51 ` [PATCH 2/8] KVM: arm64: Remove leftover kern_hyp_va() in nVHE TLB invalidation Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-11-02 13:30 ` Alexandru Elisei
2020-11-02 13:30 ` Alexandru Elisei
2020-11-02 13:30 ` Alexandru Elisei
2020-10-26 9:51 ` [PATCH 3/8] KVM: arm64: Drop useless PAN setting on host EL1 to EL2 transition Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 10:48 ` Vladimir Murzin
2020-10-26 10:48 ` Vladimir Murzin
2020-10-26 10:48 ` Vladimir Murzin
2020-10-26 9:51 ` [PATCH 4/8] KVM: arm64: Add kimg_hyp_va() helper Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` [PATCH 5/8] KVM: arm64: Turn host HVC handling into a dispatch table Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-11-02 14:19 ` Alexandru Elisei
2020-11-02 14:19 ` Alexandru Elisei
2020-11-02 14:19 ` Alexandru Elisei
2020-10-26 9:51 ` [PATCH 6/8] KVM: arm64: Patch kimage_voffset instead of loading the EL1 value Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` [PATCH 7/8] KVM: arm64: Simplify __kvm_enable_ssbs() Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-11-02 15:30 ` Alexandru Elisei
2020-11-02 15:30 ` Alexandru Elisei
2020-11-02 15:30 ` Alexandru Elisei
2020-10-26 9:51 ` [PATCH 8/8] KVM: arm64: Avoid repetitive stack access on host EL1 to EL2 exception Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-10-26 9:51 ` Marc Zyngier
2020-11-02 16:28 ` Alexandru Elisei
2020-11-02 16:28 ` Alexandru Elisei
2020-11-02 16:28 ` Alexandru Elisei
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