From: Shaokun Zhang <firstname.lastname@example.org>
To: Marc Zyngier <email@example.com>
Alex Williamson <firstname.lastname@example.org>,
Cornelia Huck <email@example.com>,
Nianyao Tang <firstname.lastname@example.org>,
Bjorn Helgaas <email@example.com>
Subject: Re: Question on guest enable msi fail when using GICv4/4.1
Date: Fri, 7 May 2021 17:58:23 +0800 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
Thanks for your quick reply.
On 2021/5/7 17:03, Marc Zyngier wrote:
> On Fri, 07 May 2021 06:57:04 +0100,
> Shaokun Zhang <email@example.com> wrote:
>> [This letter comes from Nianyao Tang]
>> Using GICv4/4.1 and msi capability, guest vf driver requires 3
>> vectors and enable msi, will lead to guest stuck.
> Stuck how?
Guest serial does not response anymore and guest network shutdown.
>> Qemu gets number of interrupts from Multiple Message Capable field
>> set by guest. This field is aligned to a power of 2(if a function
>> requires 3 vectors, it initializes it to 2).
> So I guess this is a MultiMSI device with 4 vectors, right?
Yes, it can support maximum of 32 msi interrupts, and vf driver only use 3 msi.
>> However, guest driver just sends 3 mapi-cmd to vits and 3 ite
>> entries is recorded in host. Vfio initializes msi interrupts using
>> the number of interrupts 4 provide by qemu. When it comes to the
>> 4th msi without ite in vits, in irq_bypass_register_producer,
>> producer and consumer will __connect fail, due to find_ite fail, and
>> do not resume guest.
> Let me rephrase this to check that I understand it:
> - The device has 4 vectors
> - The guest only create mappings for 3 of them
> - VFIO calls kvm_vgic_v4_set_forwarding() for each vector
> - KVM doesn't have a mapping for the 4th vector and returns an error
> - VFIO disable this 4th vector
> Is that correct? If yes, I don't understand why that impacts the guest
> at all. From what I can see, vfio_msi_set_vector_signal() just prints
> a message on the console and carries on.
in __connect, add_producer finally calls kvm_vgic_v4_set_forwarding and fails to
get the 4th mapping. When add_producer fail, it does not call cons->start, calls
kvm_arch_irq_bypass_start and then kvm_arm_resume_guest.
>> Do we support this case, Guest function using msi interrupts number
>> not aligned to a power of 2? Or qemu should provide correct msi
>> interrupts number?
> QEMU cannot know how many vectors are in use, and the guest is free to
> issue mappings for the exact number of vectors it wants to service.
> Please describe what breaks the guest here.
next prev parent reply other threads:[~2021-05-07 9:58 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-07 5:57 Question on guest enable msi fail when using GICv4/4.1 Shaokun Zhang
2021-05-07 9:03 ` Marc Zyngier
2021-05-07 9:58 ` Shaokun Zhang [this message]
2021-05-07 11:02 ` Marc Zyngier
[not found] ` <firstname.lastname@example.org>
2021-05-08 1:51 ` Jason Wang
2021-05-08 6:56 ` Zhu, Lingshan
2021-05-08 9:15 ` Marc Zyngier
2021-05-09 17:00 ` Auger Eric
2021-05-10 7:49 ` Marc Zyngier
2021-05-10 8:29 ` Auger Eric
2021-05-10 9:59 ` Marc Zyngier
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:
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
* 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).