linux-kernel - Re: [PATCH v5 00/38] New page table range API

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Message-ID: <8cfc3eef-e387-88e1-1006-2d7d97a09213@linux.ibm.com>
Date:   Tue, 11 Jul 2023 11:07:06 +0200
From:   Christian Borntraeger <borntraeger@...ux.ibm.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>
Subject: Re: [PATCH v5 00/38] New page table range API

Am 10.07.23 um 22:43 schrieb Matthew Wilcox (Oracle):
> This patchset changes the API used by the MM to set up page table entries.
> The four APIs are:
>      set_ptes(mm, addr, ptep, pte, nr)
>      update_mmu_cache_range(vma, addr, ptep, nr)
>      flush_dcache_folio(folio)
>      flush_icache_pages(vma, page, nr)
> 
> flush_dcache_folio() isn't technically new, but no architecture
> implemented it, so I've done that for them.  The old APIs remain around
> but are mostly implemented by calling the new interfaces.
> 
> The new APIs are based around setting up N page table entries at once.
> The N entries belong to the same PMD, the same folio and the same VMA,
> so ptep++ is a legitimate operation, and locking is taken care of for
> you.  Some architectures can do a better job of it than just a loop,
> but I have hesitated to make too deep a change to architectures I don't
> understand well.
> 
> One thing I have changed in every architecture is that PG_arch_1 is now a
> per-folio bit instead of a per-page bit.  This was something that would
> have to happen eventually, and it makes sense to do it now rather than
> iterate over every page involved in a cache flush and figure out if it
> needs to happen.

I think we do use PG_arch_1 on s390 for our secure page handling and
making this perf folio instead of physical page really seems wrong
and it probably breaks this code.

Claudio, can you have a look?