LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Raghavendra Rao Ananta <rananta@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Andrew Jones <drjones@redhat.com>,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Peter Shier <pshier@google.com>,
	Ricardo Koller <ricarkol@google.com>,
	Oliver Upton <oupton@google.com>,
	Reiji Watanabe <reijiw@google.com>,
	Jing Zhang <jingzhangos@google.com>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org
Subject: Re: [RFC PATCH v2 03/11] KVM: Introduce kvm_vm_has_run_once
Date: Tue, 23 Nov 2021 10:48:21 -0800	[thread overview]
Message-ID: <CAJHc60yF6BbeQGsYsSLMKd_A1SAVBiZLXBdWMO9NFH1Y2h4JRg@mail.gmail.com> (raw)
In-Reply-To: <87y25gcfti.wl-maz@kernel.org>

On Mon, Nov 22, 2021 at 8:31 AM Marc Zyngier <maz@kernel.org> wrote:
>
> On Sat, 13 Nov 2021 01:22:26 +0000,
> Raghavendra Rao Ananta <rananta@google.com> wrote:
> >
> > The upcoming patches need a way to detect if the VM, as
> > a whole, has started. Hence, unionize kvm_vcpu_has_run_once()
> > of all the vcpus of the VM and build kvm_vm_has_run_once()
> > to achieve the functionality.
> >
> > No functional change intended.
> >
> > Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> > ---
> >  include/linux/kvm_host.h |  2 ++
> >  virt/kvm/kvm_main.c      | 17 +++++++++++++++++
> >  2 files changed, 19 insertions(+)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index b373929c71eb..102e00c0e21c 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -1854,4 +1854,6 @@ static inline bool kvm_vcpu_has_run_once(struct kvm_vcpu *vcpu)
> >       return vcpu->has_run_once;
> >  }
> >
> > +bool kvm_vm_has_run_once(struct kvm *kvm);
> > +
> >  #endif
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 1ec8a8e959b2..3d8d96e8f61d 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -4339,6 +4339,23 @@ static int kvm_vm_ioctl_get_stats_fd(struct kvm *kvm)
> >       return fd;
> >  }
> >
> > +bool kvm_vm_has_run_once(struct kvm *kvm)
> > +{
> > +     int i, ret = false;
> > +     struct kvm_vcpu *vcpu;
> > +
> > +     mutex_lock(&kvm->lock);
> > +
> > +     kvm_for_each_vcpu(i, vcpu, kvm) {
> > +             ret = kvm_vcpu_has_run_once(vcpu);
> > +             if (ret)
> > +                     break;
> > +     }
> > +
> > +     mutex_unlock(&kvm->lock);
> > +     return ret;
> > +}
>
> This is horribly racy. Nothing prevents a vcpu from running behind
> your back. If you want any sort of guarantee, look at what we do in
> kvm_vgic_create(). Alexandru has patches that extract it to make it
> generally available (at least for arm64).
>
Yes, I looked into kvm_lock_all_vcpus(), but the fact that the series
would call the function with the current vcpu lock held caused me to
back off..
Perhaps I can come up with a similar function, kvm_lock_all_vcpus_except(vcpu) ?

Regards,
Raghavendra

>         M.
>
> --
> Without deviation from the norm, progress is not possible.

  reply	other threads:[~2021-11-23 18:48 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-13  1:22 [RFC PATCH v2 00/11] KVM: arm64: Add support for hypercall services selection Raghavendra Rao Ananta
2021-11-13  1:22 ` [RFC PATCH v2 01/11] KVM: arm64: Factor out firmware register handling from psci.c Raghavendra Rao Ananta
2021-11-27 13:16   ` Andrew Jones
2021-11-30  0:57     ` Raghavendra Rao Ananta
2021-11-13  1:22 ` [RFC PATCH v2 02/11] KVM: Introduce kvm_vcpu_has_run_once Raghavendra Rao Ananta
2021-11-22 16:27   ` Marc Zyngier
2021-11-23 18:31     ` Raghavendra Rao Ananta
2021-11-13  1:22 ` [RFC PATCH v2 03/11] KVM: Introduce kvm_vm_has_run_once Raghavendra Rao Ananta
2021-11-22 16:31   ` Marc Zyngier
2021-11-23 18:48     ` Raghavendra Rao Ananta [this message]
2021-11-13  1:22 ` [RFC PATCH v2 04/11] KVM: arm64: Setup a framework for hypercall bitmap firmware registers Raghavendra Rao Ananta
2021-11-22 17:23   ` Marc Zyngier
2021-11-23 18:34     ` Raghavendra Rao Ananta
2021-11-27 17:27       ` Andrew Jones
2021-11-30  0:56         ` Raghavendra Rao Ananta
2021-11-30 10:19           ` Andrew Jones
2021-11-13  1:22 ` [RFC PATCH v2 05/11] KVM: arm64: Add standard hypervisor firmware register Raghavendra Rao Ananta
2021-11-13  1:22 ` [RFC PATCH v2 06/11] KVM: arm64: Add vendor " Raghavendra Rao Ananta
2021-11-13  1:22 ` [RFC PATCH v2 07/11] Docs: KVM: Add doc for the bitmap firmware registers Raghavendra Rao Ananta
2021-11-13  1:22 ` [RFC PATCH v2 08/11] Docs: KVM: Rename psci.rst to hypercalls.rst Raghavendra Rao Ananta
2021-11-13  1:22 ` [RFC PATCH v2 09/11] tools: Import ARM SMCCC definitions Raghavendra Rao Ananta
2021-11-13  1:22 ` [RFC PATCH v2 10/11] selftests: KVM: aarch64: Introduce hypercall ABI test Raghavendra Rao Ananta
2021-11-13  1:22 ` [RFC PATCH v2 11/11] selftests: KVM: aarch64: Add the bitmap firmware registers to get-reg-list Raghavendra Rao Ananta

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=CAJHc60yF6BbeQGsYsSLMKd_A1SAVBiZLXBdWMO9NFH1Y2h4JRg@mail.gmail.com \
    --to=rananta@google.com \
    --cc=alexandru.elisei@arm.com \
    --cc=catalin.marinas@arm.com \
    --cc=drjones@redhat.com \
    --cc=james.morse@arm.com \
    --cc=jingzhangos@google.com \
    --cc=kvm@vger.kernel.org \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=maz@kernel.org \
    --cc=oupton@google.com \
    --cc=pbonzini@redhat.com \
    --cc=pshier@google.com \
    --cc=reijiw@google.com \
    --cc=ricarkol@google.com \
    --cc=suzuki.poulose@arm.com \
    --cc=will@kernel.org \
    --subject='Re: [RFC PATCH v2 03/11] KVM: Introduce kvm_vm_has_run_once' \
    /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

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).