linux-kernel - Re: [PATCH RFC v2 03/29] mm: asi: Introduce ASI core API

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Message-ID: <20250319152334.GLZ9rhdrBYW2yXRbY3@fat_crate.local>
Date: Wed, 19 Mar 2025 16:23:34 +0100
From: Borislav Petkov <bp@...en8.de>
To: Junaid Shahid <junaids@...gle.com>
Cc: Brendan Jackman <jackmanb@...gle.com>, akpm@...ux-foundation.org,
	dave.hansen@...ux.intel.com, yosryahmed@...gle.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, peterz@...radead.org, seanjc@...gle.com,
	tglx@...utronix.de, x86@...nel.org
Subject: Re: [PATCH RFC v2 03/29] mm: asi: Introduce ASI core API

On Tue, Mar 18, 2025 at 03:48:47PM -0700, Junaid Shahid wrote:
> > Oh. Yeah. In my proposal below I had totally forgotten we had
> > asi_exit() in the context_switch() path (it is there in this patch).
> > 
> > So we only need the asi_exit() in the KVM code in order to avoid
> > actually hitting e.g. exit_to_user_mode() in the restricted address
> > space.
> > 
> > But... we can just put an asi_exit() there explicitly instead of
> > dumping all this weirdness into the "core API" and the KVM codebase.
> > 
> > So... I think all we really need is asi_start_critical() and
> > asi_end_critical()? And make everything else happen as part of the
> > normal functioning of the entry and context-switching logic. Am I
> > forgetting something else?
> 
> Yes, I think this should work.

Ok, what I read so far makes sense to me. That thing - modulo simplification
but even without it - is kinda clear and straight-forward:

ioctl(KVM_RUN) {
    enter_from_user_mode()
    asi_start()
    while !need_userspace_handling()
        asi_start_critical();
        vmenter();
        asi_end_critical();
    }
    asi_end()
    exit_to_user_mode()
}

Lemme continue through the set.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette