linux-kernel - Re: [RFC 0/5] parker: PARtitioned KERnel

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Message-ID: <AEC34AE1-AEB5-4678-AC9D-39155E97D86C@zytor.com>
Date: Wed, 24 Sep 2025 12:01:52 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Dave Hansen <dave.hansen@...el.com>, Fam Zheng <fam.zheng@...edance.com>,
        linux-kernel@...r.kernel.org
CC: Lukasz Luba <lukasz.luba@....com>, linyongting@...edance.com,
        songmuchun@...edance.com, satish.kumar@...edance.com,
        Borislav Petkov <bp@...en8.de>, Thomas Gleixner <tglx@...utronix.de>,
        yuanzhu@...edance.com, Ingo Molnar <mingo@...hat.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>, fam@...hon.net, x86@...nel.org,
        liangma@...edance.com, Dave Hansen <dave.hansen@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>, guojinhui.liam@...edance.com,
        linux-pm@...r.kernel.org, Thom Hughes <thom.hughes@...edance.com>
Subject: Re: [RFC 0/5] parker: PARtitioned KERnel

On September 24, 2025 8:22:54 AM PDT, Dave Hansen <dave.hansen@...el.com> wrote:
>On 9/23/25 08:31, Fam Zheng wrote:
>> In terms of fault isolation or security, all kernel instances share
>> the same domain, as there is no supervising mechanism. A kernel bug
>> in any partition can cause problems for the whole physical machine.
>> This is a tradeoff for low-overhead / low-complexity, but hope in
>> the future we can take advantage of some hardware mechanism to
>> introduce some isolation.
>I just don't think this is approach is viable. The buck needs to stop
>_somewhere_. You can't just have a bunch of different kernels, with
>nothing in charge of the system as a whole.
>
>Just think of bus locks. They affect the whole system. What if one
>kernel turns off split lock detection? Or has a different rate limit
>than the others? What if one kernel is a big fan of WBINVD? How about
>when they use resctrl to partition an L3 cache? How about microcode updates?
>
>I'd just guess that there are a few hundred problems like that. Maybe more.
>
>I'm not saying this won't be useful for a handful of folks in a tightly
>controlled environment. But I just don't think it has a place in
>mainline where it needs to work for everyone.

Again, this comes down to why a partitioning top level hypervisor is The Right Thing[TM].

IBM mainframes are, again, the archetype here, having done it standard since VM/370 in 1972. This was running on machines with a *maximum* of 4 MB memory.

This approach works.

Nearly every OS on these machines tend to run under a *second* level hypervisor, although that isn't required.