From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Rian Quinn <rianquinn@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: x86_64 INIT/SIPI Bug
Date: Fri, 9 Nov 2018 10:42:37 -0800 [thread overview]
Message-ID: <20181109184237.GA4051@linux.intel.com> (raw)
In-Reply-To: <CANmpu8Xuuuqhfa8Tspgd9cHXetNCBkRGuGfFFSovB1A1We=n+A@mail.gmail.com>
On Fri, Nov 09, 2018 at 11:04:59AM -0700, Rian Quinn wrote:
> >> I apologize upfront if this is the wrong place to post this, pretty new to this.
> >>
> >> We are working on the Bareflank Hypervisor (www.bareflank.org), and we
> >> are passing through the INIT/SIPI process (similar to how a VMX
> >> rootkit from EFI might boot the OS) and we noticed that on Arch Linux,
> >> the INIT/SIPI process stalls, something we are not seeing on Ubuntu.
> >
> > I'm confused, INIT is blocked post-VMXON, what are you passing through?
>
> You are correct that INIT will track unconditionally, but all we do is set the
> activity state to wait-for-sipi and return back, allowing Linux to continue
> its boot process.
That's not pass-through, maybe call it reflection? I realize I'm being
a bit pedantic, but differentiating between the two matters since true
pass-through gives you bare metal performance whereas reflection obviously
requires a round-trip VMX transition.
Most hypervisors don't need a delay because they don't pass-through the
local APIC and instead emulate INIT/SIPI/SIPI. In other words, forcing
a delay for all hypervisors is unwarranted.
The correct fix is probably to add a new hook to struct x86_hyper_init
to provide a custom init delay, and add Bareflank as a new hypervisor.
prev parent reply other threads:[~2018-11-09 18:42 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-08 22:23 x86_64 INIT/SIPI Bug Rian Quinn
2018-11-09 1:16 ` Eric W. Biederman
2018-11-09 16:13 ` Rian Quinn
2018-11-09 17:49 ` Sean Christopherson
2018-11-09 18:04 ` Rian Quinn
2018-11-09 18:42 ` Sean Christopherson [this message]
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