From: Mike Rapoport <rppt@linux.ibm.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: "Steven Price" <steven.price@arm.com>,
"Mark Rutland" <Mark.Rutland@arm.com>,
x86@kernel.org, "Arnd Bergmann" <arnd@arndb.de>,
"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Will Deacon" <will.deacon@arm.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
"Jérôme Glisse" <jglisse@redhat.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"Andy Lutomirski" <luto@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"James Morse" <james.morse@arm.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
linux-arm-kernel@lists.infradead.org, "Liang,
Kan" <kan.liang@linux.intel.com>
Subject: Re: [PATCH v2 03/13] mm: Add generic p?d_large() macros
Date: Fri, 1 Mar 2019 13:49:53 +0200 [thread overview]
Message-ID: <20190301114953.GD5156@rapoport-lnx> (raw)
In-Reply-To: <20190221145706.zqwfdoyiirn3lc7y@kshutemo-mobl1>
Hi Kirill,
On Thu, Feb 21, 2019 at 05:57:06PM +0300, Kirill A. Shutemov wrote:
> On Thu, Feb 21, 2019 at 02:46:18PM +0000, Steven Price wrote:
> > On 21/02/2019 14:28, Kirill A. Shutemov wrote:
> > > On Thu, Feb 21, 2019 at 11:34:52AM +0000, Steven Price wrote:
> > >> From: James Morse <james.morse@arm.com>
> > >>
> > >> Exposing the pud/pgd levels of the page tables to walk_page_range() means
> > >> we may come across the exotic large mappings that come with large areas
> > >> of contiguous memory (such as the kernel's linear map).
> > >>
> > >> For architectures that don't provide p?d_large() macros, provided a
> > >> does nothing default.
> > >
> > > Nak, sorry.
> > >
> > > Power will get broken by the patch. It has pmd_large() inline function,
> > > that will be overwritten by the define from this patch.
> > >
> > > I believe it requires more ground work on arch side in general.
> > > All architectures that has huge page support has to provide these helpers
> > > (and matching defines) before you can use it in a generic code.
> >
> > Sorry about that, I had compile tested on power, but obviously not the
> > right config to actually see the breakage.
>
> I don't think you'll catch it at compile-time. It would silently override
> the helper with always-false.
Can you explain why the compiler would override the helper define in, e.g.
arch/powerpc/include/asm/pgtable.h with the generic (0)?
Actually, I've tried to compile this on power with deliberately adding
errors to both power-specific and the generic definition of pmd_large and
the compilation failed the way I expected in the power-specific helper.
> > I'll do some grepping - hopefully this is just a case of exposing the
> > functions/defines that already exist for those architectures.
>
> I see the same type of breakage on s390 and sparc.
>
> > Note that in terms of the new page walking code, these new defines are
> > only used when walking a page table without a VMA (which isn't currently
> > done), so architectures which don't use p?d_large currently will work
> > fine with the generic versions. They only need to provide meaningful
> > definitions when switching to use the walk-without-a-VMA functionality.
>
> How other architectures would know that they need to provide the helpers
> to get walk-without-a-VMA functionality? This looks very fragile to me.
>
> --
> Kirill A. Shutemov
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2019-03-01 11:50 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-21 11:34 [PATCH v2 00/13] Convert x86 & arm64 to use generic page walk Steven Price
2019-02-21 11:34 ` [PATCH v2 01/13] arm64: mm: Add p?d_large() definitions Steven Price
2019-02-21 13:52 ` Mark Rutland
2019-02-21 11:34 ` [PATCH v2 02/13] x86/mm: " Steven Price
2019-02-21 14:21 ` Kirill A. Shutemov
2019-02-21 11:34 ` [PATCH v2 03/13] mm: Add generic p?d_large() macros Steven Price
2019-02-21 13:41 ` Mark Rutland
2019-02-21 14:28 ` Kirill A. Shutemov
2019-02-21 14:46 ` Steven Price
2019-02-21 14:57 ` Kirill A. Shutemov
2019-02-21 17:16 ` Steven Price
2019-02-21 21:06 ` Kirill A. Shutemov
2019-02-22 10:21 ` Steven Price
2019-03-01 11:53 ` Mike Rapoport
2019-03-01 12:30 ` Kirill A. Shutemov
2019-03-01 13:39 ` Steven Price
2019-03-03 7:12 ` Mike Rapoport
2019-03-04 14:35 ` Steven Price
2019-03-04 14:53 ` Mike Rapoport
2019-03-01 11:49 ` Mike Rapoport [this message]
2019-03-01 12:28 ` Kirill A. Shutemov
2019-02-21 11:34 ` [PATCH v2 04/13] mm: pagewalk: Add p4d_entry() and pgd_entry() Steven Price
2019-02-21 11:34 ` [PATCH v2 05/13] mm: pagewalk: Allow walking without vma Steven Price
2019-02-21 11:34 ` [PATCH v2 06/13] mm: pagewalk: Add 'depth' parameter to pte_hole Steven Price
2019-02-21 11:34 ` [PATCH v2 07/13] mm: pagewalk: Add test_p?d callbacks Steven Price
2019-02-21 11:34 ` [PATCH v2 08/13] arm64: mm: Convert mm/dump.c to use walk_page_range() Steven Price
2019-02-21 11:34 ` [PATCH v2 09/13] x86/mm: Point to struct seq_file from struct pg_state Steven Price
2019-02-21 11:34 ` [PATCH v2 10/13] x86/mm+efi: Convert ptdump_walk_pgd_level() to take a mm_struct Steven Price
2019-02-21 11:35 ` [PATCH v2 11/13] x86/mm: Convert ptdump_walk_pgd_level_debugfs() to take an mm_struct Steven Price
2019-02-21 11:35 ` [PATCH v2 12/13] x86/mm: Convert ptdump_walk_pgd_level_core() " Steven Price
2019-02-21 11:35 ` [PATCH v2 13/13] x86: mm: Convert dump_pagetables to use walk_page_range Steven Price
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