linux-kernel - Re: [PATCH 2/7] x86/mm: Drop page table entry address output from pxd

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Message-ID: <8e8a94d4-39fe-4c34-9f5d-5b347ca8fe9a@intel.com>
Date: Fri, 13 Sep 2024 10:21:24 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
 "Mike Rapoport (IBM)" <rppt@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 x86@...nel.org, linux-m68k@...ts.linux-m68k.org,
 linux-fsdevel@...r.kernel.org, kasan-dev@...glegroups.com,
 linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 2/7] x86/mm: Drop page table entry address output from
 pxd_ERROR()

On 9/13/24 01:44, Anshuman Khandual wrote:
> This drops page table entry address output from all pxd_ERROR() definitions
> which now matches with other architectures. This also prevents build issues
> while transitioning into pxdp_get() based page table entry accesses.

Could you be a _little_ more specific than "build issues"?  Is it that
you want to do:

 void pmd_clear_bad(pmd_t *pmd)
 {
-        pmd_ERROR(*pmd);
+        pmd_ERROR(pmdp_get(pmd));
         pmd_clear(pmd);
 }

But the pmd_ERROR() macro would expand that to:

	&pmdp_get(pmd)

which is nonsense?

Having the PTEs' kernel addresses _is_ handy, but I guess they're
scrambled on most end users' systems now and anybody that's actively
debugging can just use a kprobe or something to dump the pmd_clear_bad()
argument directly.