From: Will Deacon <will@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>,
"maz@kernel.org" <maz@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@arm.com" <Alexandru.Elisei@arm.com>,
"qperret@google.com" <qperret@google.com>,
Linuxarm <linuxarm@huawei.com>
Subject: Re: [PATCH v3 4/4] KVM: arm64: Clear active_vmids on vCPU schedule out
Date: Tue, 3 Aug 2021 16:30:37 +0100 [thread overview]
Message-ID: <20210803153036.GA31125@willie-the-truck> (raw)
In-Reply-To: <ee2863107d614ef8a36006b5aa912eca@huawei.com>
On Tue, Aug 03, 2021 at 12:55:25PM +0000, Shameerali Kolothum Thodi wrote:
> > > diff --git a/arch/arm64/kvm/vmid.c b/arch/arm64/kvm/vmid.c
> > > index 5584e84aed95..5fd51f5445c1 100644
> > > --- a/arch/arm64/kvm/vmid.c
> > > +++ b/arch/arm64/kvm/vmid.c
> > > @@ -116,6 +116,12 @@ static u64 new_vmid(struct kvm_vmid
> > *kvm_vmid)
> > > return idx2vmid(vmid) | generation;
> > > }
> > >
> > > +/* Call with preemption disabled */
> > > +void kvm_arm_vmid_clear_active(void)
> > > +{
> > > + atomic64_set(this_cpu_ptr(&active_vmids), 0);
> > > +}
> >
> > I think this is very broken, as it will force everybody to take the
> > slow-path when they see an active_vmid of 0.
>
> Yes. I have seen that happening in my test setup.
Why didn't you say so?!
> > It also doesn't solve the issue I mentioned before, as an active_vmid of 0
> > means that the reserved vmid is preserved.
> >
> > Needs more thought...
>
> How about we clear all the active_vmids in kvm_arch_free_vm() if it
> matches the kvm_vmid->id ? But we may have to hold the lock
> there
I think we have to be really careful not to run into the "suspended
animation" problem described in ae120d9edfe9 ("ARM: 7767/1: let the ASID
allocator handle suspended animation") if we go down this road.
Maybe something along the lines of:
ROLLOVER
* Take lock
* Inc generation
=> This will force everybody down the slow path
* Record active VMIDs
* Broadcast TLBI
=> Only active VMIDs can be dirty
=> Reserve active VMIDs and mark as allocated
VCPU SCHED IN
* Set active VMID
* Check generation
* If mismatch then:
* Take lock
* Try to match a reserved VMID
* If no reserved VMID, allocate new
VCPU SCHED OUT
* Clear active VMID
but I'm not daft enough to think I got it right first time. I think it
needs both implementing *and* modelling in TLA+ before we merge it!
Will
next prev parent reply other threads:[~2021-08-03 15:30 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-29 10:40 [PATCH v3 0/4] kvm/arm: New VMID allocator based on asid Shameer Kolothum
2021-07-29 10:40 ` [PATCH v3 1/4] KVM: arm64: Introduce a new VMID allocator for KVM Shameer Kolothum
2021-08-03 11:38 ` Will Deacon
2021-08-03 12:12 ` Shameerali Kolothum Thodi
2021-07-29 10:40 ` [PATCH v3 2/4] KVM: arm64: Make VMID bits accessible outside of allocator Shameer Kolothum
2021-07-29 10:40 ` [PATCH v3 3/4] KVM: arm64: Align the VMID allocation with the arm64 ASID one Shameer Kolothum
2021-07-29 14:59 ` kernel test robot
2021-07-29 10:40 ` [PATCH v3 4/4] KVM: arm64: Clear active_vmids on vCPU schedule out Shameer Kolothum
2021-08-03 11:40 ` Will Deacon
2021-08-03 12:55 ` Shameerali Kolothum Thodi
2021-08-03 15:30 ` Will Deacon [this message]
2021-08-03 15:56 ` Shameerali Kolothum Thodi
2021-08-06 12:24 ` Shameerali Kolothum Thodi
2021-08-09 13:09 ` Will Deacon
2021-08-09 13:48 ` Shameerali Kolothum Thodi
2021-08-11 8:47 ` Shameerali Kolothum Thodi
2021-10-11 6:06 ` Shameerali Kolothum Thodi
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210803153036.GA31125@willie-the-truck \
--to=will@kernel.org \
--cc=Alexandru.Elisei@arm.com \
--cc=catalin.marinas@arm.com \
--cc=james.morse@arm.com \
--cc=jean-philippe@linaro.org \
--cc=julien.thierry.kdev@gmail.com \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxarm@huawei.com \
--cc=maz@kernel.org \
--cc=qperret@google.com \
--cc=shameerali.kolothum.thodi@huawei.com \
--cc=suzuki.poulose@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).