Message-ID: <5d99c731-c47a-c525-76e5-4578d9dfc9ee@redhat.com>
Date:   Tue, 28 Feb 2023 16:55:41 +0100
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Subject: Re: [PATCH mm-unstable v1 11/26] microblaze/mm: support
 __HAVE_ARCH_PTE_SWP_EXCLUSIVE
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To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Yang Shi <shy828301@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Nadav Amit <namit@vmware.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Peter Xu <peterx@redhat.com>, linux-mm@kvack.org,
        x86@kernel.org, linux-alpha@vger.kernel.org,
        linux-snps-arc@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org,
        linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org,
        loongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org,
        linux-mips@vger.kernel.org, openrisc@lists.librecores.org,
        linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
        linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
        linux-um@lists.infradead.org, linux-xtensa@linux-xtensa.org,
        Michal Simek <monstr@monstr.eu>
References: <20230113171026.582290-1-david@redhat.com>
 <20230113171026.582290-12-david@redhat.com>
 <CAMuHMdX-FDga8w=pgg1myskEx6wp+oyZifhPPPFnWrc1zW7ZpQ@mail.gmail.com>
 <9ed766a6-cf06-535d-3337-ea6ff25c2362@redhat.com>
 <CAMuHMdWSaoKqO1Nx7QMDCcXrRmFbqqX8uwDRezXs8g+HdEFjKA@mail.gmail.com>
 <c145a2db-f92c-65aa-3e68-07dbb2e097a6@redhat.com>
 <CAMuHMdX7MND++KXgTpx4jscfctQA_-zPt3EN9-+79EWE7e+OjA@mail.gmail.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <CAMuHMdX7MND++KXgTpx4jscfctQA_-zPt3EN9-+79EWE7e+OjA@mail.gmail.com>
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On 27.02.23 20:46, Geert Uytterhoeven wrote:
> Hi David,
> 
> On Mon, Feb 27, 2023 at 6:01 PM David Hildenbrand <david@redhat.com> wrote:
>>>>>>     /*
>>>>>>      * Externally used page protection values.
>>>>>> diff --git a/arch/microblaze/include/asm/pgtable.h b/arch/microblaze/include/asm/pgtable.h
>>>>>> index 42f5988e998b..7e3de54bf426 100644
>>>>>> --- a/arch/microblaze/include/asm/pgtable.h
>>>>>> +++ b/arch/microblaze/include/asm/pgtable.h
> 
>>>>>>      * - All other bits of the PTE are loaded into TLBLO without
>>>>>>      *  * modification, leaving us only the bits 20, 21, 24, 25, 26, 30 for
>>>>>>      * software PTE bits.  We actually use bits 21, 24, 25, and
>>>>>> @@ -155,6 +155,9 @@ extern pte_t *va_to_pte(unsigned long address);
>>>>>>     #define _PAGE_ACCESSED 0x400   /* software: R: page referenced */
>>>>>>     #define _PMD_PRESENT   PAGE_MASK
>>>>>>
>>>>>> +/* We borrow bit 24 to store the exclusive marker in swap PTEs. */
>>>>>> +#define _PAGE_SWP_EXCLUSIVE    _PAGE_DIRTY
>>>>>
>>>>> _PAGE_DIRTY is 0x80, so this is also bit 7, thus the new comment is
>>>>> wrong?
>>>>
>>>> In the example, I use MSB-0 bit numbering (which I determined to be
>>>> correct in microblaze context eventually, but I got confused a couple a
>>>> times because it's very inconsistent). That should be MSB-0 bit 24.
>>>
>>> Thanks, TIL microblaze uses IBM bit numbering...
>>
>> I assume IBM bit numbering corresponds to MSB-0 bit numbering, correct?
> 
> Correct, as seen in s370 and PowerPC manuals...

Good, I have some solid s390x background, but thinking about the term 
"IBM PC" made me double-check that we're talking about the same thing ;)

> 
>> I recall that I used the comment above "/* Definitions for MicroBlaze.
>> */" as an orientation.
>>
>> 0  1  2  3  4  ... 18 19 20 21 22 23 24 25 26 27 28 29 30 31
>> RPN.....................  0  0 EX WR ZSEL.......  W  I  M  G
> 
> Indeed, that's where I noticed the "unconventional" numbering...
> 
>> So ... either we adjust both or we leave it as is. (again, depends on
>> what the right thing to to is -- which I don't know :) )
> 
> It depends whether you want to match the hardware documentation,
> or the Linux BIT() macro and friends...

The hardware documentation, so we should be good.

Thanks!

-- 
Thanks,

David / dhildenb