From: Marc Zyngier <maz@kernel.org>
To: Steven Price <steven.price@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Dave Martin <Dave.Martin@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
Richard Henderson <richard.henderson@linaro.org>,
Peter Maydell <peter.maydell@linaro.org>,
Haibo Xu <Haibo.Xu@arm.com>, Andrew Jones <drjones@redhat.com>
Subject: Re: [PATCH v12 6/8] arm64: kvm: Expose KVM_ARM_CAP_MTE
Date: Thu, 20 May 2021 11:09:40 +0100 [thread overview]
Message-ID: <8735uhvhqz.wl-maz@kernel.org> (raw)
In-Reply-To: <4e1fc7b7-ea8c-a87c-9177-d9e03ff96cb8@arm.com>
On Wed, 19 May 2021 14:26:31 +0100,
Steven Price <steven.price@arm.com> wrote:
>
> On 17/05/2021 18:40, Marc Zyngier wrote:
> > On Mon, 17 May 2021 13:32:37 +0100,
> > Steven Price <steven.price@arm.com> wrote:
> >>
> >> It's now safe for the VMM to enable MTE in a guest, so expose the
> >> capability to user space.
> >>
> >> Signed-off-by: Steven Price <steven.price@arm.com>
> >> ---
> >> arch/arm64/kvm/arm.c | 9 +++++++++
> >> arch/arm64/kvm/sys_regs.c | 3 +++
> >> 2 files changed, 12 insertions(+)
> >>
> >> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> >> index 1cb39c0803a4..e89a5e275e25 100644
> >> --- a/arch/arm64/kvm/arm.c
> >> +++ b/arch/arm64/kvm/arm.c
> >> @@ -93,6 +93,12 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> >> r = 0;
> >> kvm->arch.return_nisv_io_abort_to_user = true;
> >> break;
> >> + case KVM_CAP_ARM_MTE:
> >> + if (!system_supports_mte() || kvm->created_vcpus)
> >> + return -EINVAL;
> >> + r = 0;
> >> + kvm->arch.mte_enabled = true;
> >
> > As far as I can tell from the architecture, this isn't valid for a
> > 32bit guest.
>
> Indeed, however the MTE flag is a property of the VM not of the vCPU.
> And, unless I'm mistaken, it's technically possible to create a VM where
> some CPUs are 32 bit and some 64 bit. Not that I can see much use of a
> configuration like that.
It looks that this is indeed a bug, and I'm on my way to squash it.
Can't believe we allowed that for so long...
But the architecture clearly states:
<quote>
These features are supported in AArch64 state only.
</quote>
So I'd expect something like:
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index 956cdc240148..50635eacfa43 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -220,7 +220,8 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
switch (vcpu->arch.target) {
default:
if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
- if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1)) {
+ if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) ||
+ vcpu->kvm->arch.mte_enabled) {
ret = -EINVAL;
goto out;
}
that makes it completely impossible to create 32bit CPUs within a
MTE-enabled guest.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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next prev parent reply other threads:[~2021-05-20 10:11 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-17 12:32 [PATCH v12 0/8] MTE support for KVM guest Steven Price
2021-05-17 12:32 ` [PATCH v12 1/8] arm64: mte: Handle race when synchronising tags Steven Price
2021-05-17 14:03 ` Marc Zyngier
2021-05-17 14:56 ` Steven Price
2021-05-19 17:32 ` Catalin Marinas
2021-05-17 12:32 ` [PATCH v12 2/8] arm64: Handle MTE tags zeroing in __alloc_zeroed_user_highpage() Steven Price
2021-05-17 12:32 ` [PATCH v12 3/8] arm64: mte: Sync tags for pages where PTE is untagged Steven Price
2021-05-17 16:14 ` Marc Zyngier
2021-05-19 9:32 ` Steven Price
2021-05-19 17:48 ` Catalin Marinas
2021-05-19 18:06 ` Catalin Marinas
2021-05-20 11:55 ` Steven Price
2021-05-20 12:25 ` Catalin Marinas
2021-05-20 13:02 ` Catalin Marinas
2021-05-20 13:03 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 4/8] arm64: kvm: Introduce MTE VM feature Steven Price
2021-05-17 16:45 ` Marc Zyngier
2021-05-19 10:48 ` Steven Price
2021-05-20 8:51 ` Marc Zyngier
2021-05-20 14:46 ` Steven Price
2021-05-20 11:54 ` Catalin Marinas
2021-05-20 15:05 ` Steven Price
2021-05-20 17:50 ` Catalin Marinas
2021-05-21 9:28 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 5/8] arm64: kvm: Save/restore MTE registers Steven Price
2021-05-17 17:17 ` Marc Zyngier
2021-05-19 13:04 ` Steven Price
2021-05-20 9:46 ` Marc Zyngier
2021-05-20 15:21 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 6/8] arm64: kvm: Expose KVM_ARM_CAP_MTE Steven Price
2021-05-17 17:40 ` Marc Zyngier
2021-05-19 13:26 ` Steven Price
2021-05-20 10:09 ` Marc Zyngier [this message]
2021-05-20 10:51 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 7/8] KVM: arm64: ioctl to fetch/store tags in a guest Steven Price
2021-05-17 18:04 ` Marc Zyngier
2021-05-19 13:51 ` Steven Price
2021-05-20 12:05 ` Catalin Marinas
2021-05-20 15:58 ` Steven Price
2021-05-20 17:27 ` Catalin Marinas
2021-05-21 9:42 ` Steven Price
2021-05-24 18:11 ` Catalin Marinas
2021-05-27 7:50 ` Steven Price
2021-05-27 13:08 ` Catalin Marinas
2021-05-17 12:32 ` [PATCH v12 8/8] KVM: arm64: Document MTE capability and ioctl Steven Price
2021-05-17 18:09 ` Marc Zyngier
2021-05-19 14:09 ` Steven Price
2021-05-20 10:24 ` Marc Zyngier
2021-05-20 10:52 ` Steven Price
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