linux-kernel - Re: [RFC v2 14/35] RPAL: enable page fault handling

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Message-ID: <304ea078-0f09-43d6-9dd2-264eb195e33e@intel.com>
Date: Fri, 30 May 2025 06:59:29 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Bo Li <libo.gcs85@...edance.com>, tglx@...utronix.de, mingo@...hat.com,
 bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, luto@...nel.org,
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 juri.lelli@...hat.com, vincent.guittot@...aro.org, peterz@...radead.org
Cc: dietmar.eggemann@....com, hpa@...or.com, acme@...nel.org,
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Subject: Re: [RFC v2 14/35] RPAL: enable page fault handling

On 5/30/25 02:27, Bo Li wrote:
>  arch/x86/mm/fault.c     | 271 ++++++++++++++++++++++++++++++++++++++++
>  arch/x86/rpal/mm.c      |  34 +++++
>  arch/x86/rpal/service.c |  24 ++++
>  arch/x86/rpal/thread.c  |  23 ++++
>  include/linux/rpal.h    |  81 ++++++++----
>  5 files changed, 412 insertions(+), 21 deletions(-)

I'm actually impressed again that you've managed to get this ported over
to a newer kernel _and_ broken it up.

But just taking a quick peek at _one_ patch, this is far, far below the
standards by which we do kernel development. This appears to have simply
copied chunks of existing code, hacked it to work with "RPAL" and then
#ifdef'd.

This is, unfortunately, copying and pasting at its worst. It creates
dual paths that inevitably bit rot in some way and are hard to maintain.

So, just to be clear: it's a full an unequivocal NAK from me on this
series. This introduces massive change, massive security risk, can't
possibly be backward compatible, has no users (well, maybe one) and the
series is not put together in anything remotely resembling how we like
to do kernel development.

I'd appreciate if you could not cc me on future versions if you choose
to go forward with this. But I urge you to stop now.