linux-kernel - Re: your "x86: mm: convert dump_pagetables to use walk_page

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Date:   Tue, 12 May 2020 15:09:54 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Steven Price <steven.price@....com>
Cc:     the arch/x86 maintainers <x86@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: your "x86: mm: convert dump_pagetables to use walk_page_range"
 change

On 12.05.2020 15:02, Steven Price wrote:
> On 12/05/2020 10:39, Jan Beulich wrote:
>> Additionally I'd like to note that note_page()'s "unsigned long val"
>> parameter isn't wide enough for 32-bit PAE PTEs, and hence the NX
>> flag will always be seen as clear in new_prot in such configs.
> 
> Ah, interesting. I'm not sure what type is actually guaranteed to be 
> correct. pgprotval_t is x86 specific, but it might be necessary to 
> extend it to other architectures. I think I got the "unsigned long" from 
> the generic page.h (and because it happens to work on most 
> architectures) - but hadn't noticed that that file was specifically only 
> for NOMMU architectures.

Well, it's pteval_t (still x86-specific I guess) unless the call
sites could/would be switched to use pte_flags(). As per
https://lists.xenproject.org/archives/html/xen-devel/2020-05/msg00549.html
the use of pte_val() has another bad effect, but as described
there it might also be Xen specific code which is broken here.

> I'll see if I can come up with fixes, but if you've got anything ready 
> already then please jump in.

No, I don't. I lack the time right now to make a change potentially
affecting multiple architectures.

Jan