From: Matthew Wilcox <willy@infradead.org>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
Kees Cook <keescook@chromium.org>,
Sri Krishna chowdary <schowdary@nvidia.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
x86@kernel.org, Dave Hansen <dave.hansen@intel.com>,
linux-kernel@vger.kernel.org, Steven Price <Steven.Price@arm.com>,
linux-mm@kvack.org, Mark Brown <Mark.Brown@arm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC] mm/pgtable/debug: Add test validating architecture page table helpers
Date: Fri, 26 Jul 2019 12:54:57 -0700 [thread overview]
Message-ID: <20190726195457.GI30641@bombadil.infradead.org> (raw)
In-Reply-To: <c3bb0420-584c-de3b-2439-8702bc09595e@arm.com>
On Fri, Jul 26, 2019 at 10:17:11AM +0530, Anshuman Khandual wrote:
> > But 'page' isn't necessarily PMD-aligned. I don't think we can rely on
> > architectures doing the right thing if asked to make a PMD for a randomly
> > aligned page.
> >
> > How about finding the physical address of something like kernel_init(),
>
> Physical address corresponding to the symbol in the kernel text segment ?
Yes. We need the address of something that's definitely memory.
The stack might be in vmalloc space. We can't allocate memory from the
allocator that's PUD-aligned. This seems like a reasonable approximation
to something that might work.
> > and using the corresponding pte/pmd/pud/p4d/pgd that encompasses that
>
> So I guess this will help us use pte/pmd/pud/p4d/pgd entries from a real and
> present mapping rather then making them up for test purpose. Although we are
> not creating real page tables here just wondering if this could some how
> affect these real mapping in anyway from some accessors. The current proposal
> stays clear from anything real - allocates, evaluates and releases.
I think that's a mistake. As Russell said, the ARM p*d manipulation
functions expect to operate on tables, not on individual entries
constructed on the stack.
So I think the right thing to do here is allocate an mm, then do the
pgd_alloc / p4d_alloc / pud_alloc / pmd_alloc / pte_alloc() steps giving
you real page tables that you can manipulate.
Then destroy them, of course. And don't access through them.
> >> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> >> +static void pud_basic_tests(void)
> >
> > Is this the right ifdef?
>
> IIUC THP at PUD is where the pud_t entries are directly operated upon and the
> corresponding accessors are present only when HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> is enabled. Am I missing something here ?
Maybe I am. I thought we could end up operating on PUDs for kernel mappings,
even without transparent hugepages turned on.
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next prev parent reply other threads:[~2019-07-26 19:55 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-25 6:55 [RFC] mm/debug: Add tests for architecture exported page table helpers Anshuman Khandual
2019-07-25 6:55 ` [RFC] mm/pgtable/debug: Add test validating architecture " Anshuman Khandual
2019-07-25 14:39 ` Matthew Wilcox
2019-07-25 21:38 ` Russell King - ARM Linux admin
2019-07-25 21:42 ` Matthew Wilcox
2019-07-25 21:58 ` Russell King - ARM Linux admin
2019-07-25 22:56 ` Matthew Wilcox
2019-07-26 4:47 ` Anshuman Khandual
2019-07-26 19:54 ` Matthew Wilcox [this message]
2019-07-29 8:32 ` Anshuman Khandual
2019-07-30 17:03 ` Matthew Wilcox
2019-08-05 4:35 ` Anshuman Khandual
2019-07-25 17:07 ` Catalin Marinas
2019-07-26 4:28 ` Anshuman Khandual
2019-07-25 21:54 ` Russell King - ARM Linux admin
2019-07-26 5:10 ` Anshuman Khandual
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