linux-kernel - Re: [RFC v2 4/9] x86/mm: Introduce X86_FEATURE

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Message-ID: <20250521193934.GFaC4r9h38nCeHbt26@fat_crate.local>
Date: Wed, 21 May 2025 21:39:34 +0200
From: Borislav Petkov <bp@...en8.de>
To: Rik van Riel <riel@...riel.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
	kernel-team@...a.com, dave.hansen@...ux.intel.com, luto@...nel.org,
	peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, nadav.amit@...il.com, Rik van Riel <riel@...com>,
	Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [RFC v2 4/9] x86/mm: Introduce X86_FEATURE_RAR

On Wed, May 21, 2025 at 12:06:59PM -0400, Rik van Riel wrote:
> On Wed, 2025-05-21 at 16:53 +0200, Borislav Petkov wrote:
> > On Wed, May 21, 2025 at 09:57:52AM -0400, Rik van Riel wrote:
> > > I had the same thought, and tried that already.
> > > 
> > > It didn't work.
> > 
> > Care to share why?
> > 
> It resulted in RAR not being properly initialized,
> and the system hanging when trying to use RAR to
> flush the TLB.
> 
> I don't remember exactly what sequence of events
> was happening here, maybe something with the
> boot CPU per-cpu RAR initialization being called
> (or not, due to X86_FEATURE_RAR not being set)
> before the systemwide initialization?

I'm asking you to move it from this path to

                if (this_cpu->c_early_init)
                        this_cpu->c_early_init(c);

or

                if (this_cpu->c_bsp_init)
                        this_cpu->c_bsp_init(c);

a couple of lines above.

This doesn't change anything: you're still running it on the BSP once. So
I don't see how any of the above confusion would happen.

-- 
Regards/Gruss,
    Boris.

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