linux-kernel - Re: [PATCH v4 2/5] sparc: fix accurate exception reporting in copy_{from_to}

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Message-ID: <35a07d38d6d59b79d28543bb4a862f14af1fa713.camel@physik.fu-berlin.de>
Date: Sun, 07 Sep 2025 19:57:37 +0200
From: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To: René Rebe <rene@...ctco.de>
Cc: Michael Karcher <kernel@...rcher.dialup.fu-berlin.de>, Andreas Larsson	
 <andreas@...sler.com>, sparclinux@...r.kernel.org,
 linux-kernel@...r.kernel.org,  Anthony Yznaga <anthony.yznaga@...cle.com>
Subject: Re: [PATCH v4 2/5] sparc: fix accurate exception reporting in
 copy_{from_to}_user for UltraSPARC III

Hi Rene,

On Sun, 2025-09-07 at 19:32 +0200, René Rebe wrote:
> It is probably a good time to mention that there are likely some other major
> TLB (or so) bug on U3. For example, I could never boot any Linux kernel
> (probably ever) with 8GB installed in my Sun Blade 1000 - it would NULL ptr
> deref very early:

Have a look at arch/sparc/kernel/head_64.S:

	/* Patch copy/page operations to cheetah optimized versions. */
	call	cheetah_patch_copyops
	 nop
	call	cheetah_patch_copy_page
	 nop
	call	cheetah_patch_cachetlbops
	 nop

These patch in UltraSPARC-III-optimized versions of copy_{to,from}_user
and copy_page and TLB operations. Replacing these calls with "nop" might
tell us whether any of those is broken.

I have already replaced cheetah_patch_copyops with generic_patch_copyops
and was able to verify that the recently discovered OOPS is not related
to copy_{to,from}_user, so Michael's UltraSPARC III may still be correct
and complete.

I am testing the other two now as I think that these are good candidates.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913