From: Zenghui Yu <yuzenghui@huawei.com>
To: Marc Zyngier <maz@kernel.org>,
Peter Maydell <peter.maydell@linaro.org>,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: <linux-arm-kernel@lists.infradead.org>,
<kvmarm@lists.cs.columbia.edu>, <kvm@vger.kernel.org>,
<qemu-arm@nongnu.org>, Eric Auger <eric.auger@redhat.com>
Subject: Re: [PATCH] KVM: arm/arm64: vgic: Allow more than 256 vcpus for KVM_IRQ_LINE
Date: Thu, 29 Aug 2019 10:46:57 +0800 [thread overview]
Message-ID: <47328538-01e6-3152-01f1-ae9c923f628f@huawei.com> (raw)
In-Reply-To: <20190818140710.23920-1-maz@kernel.org>
Hi Marc,
On 2019/8/18 22:07, Marc Zyngier wrote:
> While parts of the VGIC support a large number of vcpus (we
> bravely allow up to 512), other parts are more limited.
>
> One of these limits is visible in the KVM_IRQ_LINE ioctl, which
> only allows 256 vcpus to be signalled when using the CPU or PPI
> types. Unfortunately, we've cornered ourselves badly by allocating
> all the bits in the irq field.
>
> Since the irq_type subfield (8 bit wide) is currently only taking
> the values 0, 1 and 2 (and we have been careful not to allow anything
> else), let's reduce this field to only 4 bits, and allocate the
> remaining 4 bits to a vcpu2_index, which acts as a multiplier:
>
> vcpu_id = 256 * vcpu2_index + vcpu_index
>
> With that, and a new capability (KVM_CAP_ARM_IRQ_LINE_LAYOUT_2)
> allowing this to be discovered, it becomes possible to inject
> PPIs to up to 4096 vcpus. But please just don't.
>
> Reported-by: Zenghui Yu <yuzenghui@huawei.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
And tested together with Eric's patches (KVM+QEMU).
Thanks,
zenghui
next prev parent reply other threads:[~2019-08-29 2:48 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-18 14:07 [PATCH] KVM: arm/arm64: vgic: Allow more than 256 vcpus for KVM_IRQ_LINE Marc Zyngier
2019-08-19 7:41 ` Will Deacon
2019-08-19 8:46 ` Marc Zyngier
2019-08-22 9:00 ` Auger Eric
2019-08-29 2:46 ` Zenghui Yu [this message]
2019-09-03 11:33 ` Peter Maydell
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=47328538-01e6-3152-01f1-ae9c923f628f@huawei.com \
--to=yuzenghui@huawei.com \
--cc=eric.auger@redhat.com \
--cc=james.morse@arm.com \
--cc=julien.thierry.kdev@gmail.com \
--cc=kvm@vger.kernel.org \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=maz@kernel.org \
--cc=peter.maydell@linaro.org \
--cc=qemu-arm@nongnu.org \
--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).