From: Marc Zyngier <maz@kernel.org>
To: Quentin Perret <qperret@google.com>
Cc: Will Deacon <will@kernel.org>,
kvmarm@lists.linux.dev, oupton@kernel.org, joey.gouly@arm.com,
suzuki.poulose@arm.com, yuzenghui@huawei.com,
catalin.marinas@arm.com
Subject: Re: Broken udelay() on KVM host with a vcpu loaded
Date: Tue, 10 Feb 2026 19:54:36 +0000 [thread overview]
Message-ID: <86o6lwbchv.wl-maz@kernel.org> (raw)
In-Reply-To: <motrqsddhooajk66sq75dt74huvxmwtreoznwc6yjqirit36bl@2mlt2546mjnp>
On Tue, 10 Feb 2026 15:58:14 +0000,
Quentin Perret <qperret@google.com> wrote:
>
> Ouch, it does seem that the SET_ONE_REG stuff allows to mess with that
> value _out of vcpu context_, so yeah userspace could change the value
> while a vcpu thread is preempted in the middle of a udelay loop ...
I don't think so. You can only do that on the vcpu fd, and if the vcpu
is loaded, it means that you are already holding the vcpu mutex. And
if you do that from the vcpu thread, then you already have done a
vcpu_put().
M.
--
Without deviation from the norm, progress is not possible.
next prev parent reply other threads:[~2026-02-10 19:54 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-10 12:27 Broken udelay() on KVM host with a vcpu loaded Quentin Perret
2026-02-10 12:52 ` Marc Zyngier
2026-02-10 15:34 ` Will Deacon
2026-02-10 15:58 ` Quentin Perret
2026-02-10 19:54 ` Marc Zyngier [this message]
2026-02-13 11:50 ` Will Deacon
2026-02-13 13:52 ` Marc Zyngier
2026-02-13 14:05 ` Quentin Perret
2026-02-10 19:46 ` Marc Zyngier
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