From: Peter Xu <peterx@redhat.com>
To: Auger Eric <eric.auger@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Alex Williamson <alex.williamson@redhat.com>,
Cornelia Huck <cohuck@redhat.com>,
qemu-devel@nongnu.org
Subject: Re: [PATCH 0/5] vfio/pci: Fix up breakage against split irqchip and INTx
Date: Thu, 27 Feb 2020 10:51:46 -0500 [thread overview]
Message-ID: <20200227155146.GD180973@xz-x1> (raw)
In-Reply-To: <bd685da9-bc50-f901-bfec-a1cd18832307@redhat.com>
On Thu, Feb 27, 2020 at 04:32:24PM +0100, Auger Eric wrote:
> Hi Peter,
Hi, Eric,
>
> On 2/26/20 11:50 PM, Peter Xu wrote:
> > VFIO INTx is not working with split irqchip. On new kernels KVM_IRQFD
> > will directly fail with resamplefd attached so QEMU will automatically
> > fallback to the INTx slow path. However on old kernels it's still
> > broken.
> I think you should quote the commit that changes the behavior:
> 654f1f13ea56 kvm: Check irqchip mode before assign irqfd?
> so that one can understand what it fixed.
Right I should mention that.
Actually I mentioned it in an old cover letter but unluckily something
wrong happened with git-publish and merely my whole cover letter is
gone... So what you saw is actually a simplified version and I think
I must have lost something like this... :(
Thanks for bringing that up.
>
> So on kernels that do not feature that commit, the ioctl succeeds and we
> pretend the resamplefd was properly attached whereas in practice it was
> never triggered.
Right. Another thing I just noticed is that we must _not_ attach the
resamplefd to the KVM_IRQFD ioctl when we registered this in the
userspace. One thing is it's for sure not needed at all. More
importantly, on new kernels (after commit 654f1f13ea56) the KVM_IRQFD
could fail (because it sees both split irqchip and resamplefd) and
QEMU will fallback again to the slow path even if the fast path can
work.
Thanks,
--
Peter Xu
next prev parent reply other threads:[~2020-02-27 15:52 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-26 22:50 [PATCH 0/5] vfio/pci: Fix up breakage against split irqchip and INTx Peter Xu
2020-02-26 22:50 ` [PATCH 1/5] vfio/pci: Disable INTx fast path if using split irqchip Peter Xu
2020-02-27 16:53 ` Auger Eric
2020-02-27 17:10 ` Peter Xu
2020-02-26 22:50 ` [PATCH 2/5] vfio/pci: Use kvm_irqchip_add_irqfd_notifier_gsi() for irqfds Peter Xu
2020-02-27 11:04 ` Auger Eric
2020-02-27 16:41 ` Cornelia Huck
2020-02-26 22:54 ` [PATCH 3/5] KVM: Pass EventNotifier into kvm_irqchip_assign_irqfd Peter Xu
2020-02-27 17:01 ` Auger Eric
2020-02-26 22:55 ` [PATCH 4/5] KVM: Kick resamplefd for split kernel irqchip Peter Xu
2020-02-27 17:00 ` [PATCH v1.1 " Peter Xu
2020-02-27 17:18 ` Peter Xu
2020-02-27 17:42 ` Auger Eric
2020-02-27 18:00 ` Peter Xu
2020-02-27 18:22 ` Auger Eric
2020-02-27 19:19 ` Peter Xu
2020-02-27 21:14 ` Auger Eric
2020-02-27 21:52 ` Peter Xu
2020-02-28 10:34 ` Paolo Bonzini
2020-02-28 10:36 ` Auger Eric
2020-02-28 10:34 ` [PATCH " Paolo Bonzini
2020-02-28 14:58 ` Peter Xu
2020-02-28 15:24 ` Paolo Bonzini
2020-02-26 22:55 ` [PATCH 5/5] Revert "vfio/pci: Disable INTx fast path if using split irqchip" Peter Xu
2020-02-27 15:32 ` [PATCH 0/5] vfio/pci: Fix up breakage against split irqchip and INTx Auger Eric
2020-02-27 15:51 ` Peter Xu [this message]
2020-02-27 17:02 ` Peter Xu
2020-02-28 10:36 ` Paolo Bonzini
2020-02-28 15:25 ` Peter Xu
2020-02-28 15:32 ` Paolo Bonzini
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