From: Marc Zyngier <maz@kernel.org>
To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
Cc: "linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"will@kernel.org" <will@kernel.org>,
"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
"james.morse@arm.com" <james.morse@arm.com>,
"julien.thierry.kdev@gmail.com" <julien.thierry.kdev@gmail.com>,
"suzuki.poulose@arm.com" <suzuki.poulose@arm.com>,
"jean-philippe@linaro.org" <jean-philippe@linaro.org>,
Alexandru Elisei <Alexandru.Elisei@arm.com>,
Linuxarm <linuxarm@huawei.com>
Subject: Re: [RFC PATCH 0/3] kvm/arm: New VMID allocator based on asid(2nd approach)
Date: Fri, 04 Jun 2021 14:54:37 +0100 [thread overview]
Message-ID: <87sg1xzqea.wl-maz@kernel.org> (raw)
In-Reply-To: <e62829990c50479292af94c4152011fc@huawei.com>
On Fri, 04 Jun 2021 09:13:10 +0100,
Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com> wrote:
>
> Hi,
>
> > -----Original Message-----
> > From: Shameerali Kolothum Thodi
> > Sent: 06 May 2021 17:52
> > To: linux-arm-kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu;
> > linux-kernel@vger.kernel.org
> > Cc: maz@kernel.org; will@kernel.org; catalin.marinas@arm.com;
> > james.morse@arm.com; julien.thierry.kdev@gmail.com;
> > suzuki.poulose@arm.com; jean-philippe@linaro.org; Linuxarm
> > <linuxarm@huawei.com>
> > Subject: [RFC PATCH 0/3] kvm/arm: New VMID allocator based on asid(2nd
> > approach)
> >
> > This is based on a suggestion from Will [0] to try out the asid
> > based kvm vmid solution as a separate VMID allocator instead of
> > the shared lib approach attempted in v4[1].
> >
> > The idea is to compare both the approaches and see whether the
> > shared lib solution with callbacks make sense or not.
>
> A gentle ping on this. Please take a look and let me know.
I had a look and I don't overly dislike it. I'd like to see the code
without the pinned stuff though, at least to ease the reviewing. I
haven't tested it in anger, but I have pushed the rebased code at [1]
as it really didn't apply to 5.13-rc4.
One thing I'm a bit worried about is that we so far relied on VMID 0
never being allocated to a guest, which is now crucial for protected
KVM. I can't really convince myself that this can never happen with
this. Plus, I've found this nugget:
<quote
max_pinned_vmids = NUM_USER_VMIDS - num_possible_cpus() - 2;
</quote>
What is this "- 2"? My hunch is that it should really be "- 1" as VMID
0 is reserved, and we have no equivalent of KPTI for S2.
M.
[1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/mmu/vmid
--
Without deviation from the norm, progress is not possible.
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next prev parent reply other threads:[~2021-06-04 13:56 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-06 16:52 [RFC PATCH 0/3] kvm/arm: New VMID allocator based on asid(2nd approach) Shameer Kolothum
2021-05-06 16:52 ` [RFC PATCH 1/3] arch/arm64: Introduce a capability to tell whether 16-bit VMID is available Shameer Kolothum
2021-05-06 16:52 ` [RFC PATCH 2/3] kvm/arm: Introduce a new vmid allocator for KVM Shameer Kolothum
2021-05-06 16:52 ` [RFC PATCH 3/3] kvm/arm: Align the VMID allocation with the arm64 ASID one Shameer Kolothum
2021-06-04 8:13 ` [RFC PATCH 0/3] kvm/arm: New VMID allocator based on asid(2nd approach) Shameerali Kolothum Thodi
2021-06-04 13:54 ` Marc Zyngier [this message]
2021-06-04 14:51 ` Shameerali Kolothum Thodi
2021-06-04 15:27 ` Marc Zyngier
2021-06-07 8:48 ` Jean-Philippe Brucker
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