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From: Matthew Wilcox <willy@infradead.org>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
	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: Thu, 25 Jul 2019 15:56:58 -0700	[thread overview]
Message-ID: <20190725225658.GH30641@bombadil.infradead.org> (raw)
In-Reply-To: <20190725215812.GN1330@shell.armlinux.org.uk>

On Thu, Jul 25, 2019 at 10:58:12PM +0100, Russell King - ARM Linux admin wrote:
> On Thu, Jul 25, 2019 at 02:42:22PM -0700, Matthew Wilcox wrote:
> > On Thu, Jul 25, 2019 at 10:38:58PM +0100, Russell King - ARM Linux admin wrote:
> > > On Thu, Jul 25, 2019 at 07:39:21AM -0700, Matthew Wilcox 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(),
> > > > and using the corresponding pte/pmd/pud/p4d/pgd that encompasses that
> > > > address?  It's also better to pass in the pfn/page rather than using global
> > > > variables to communicate to the test functions.
> > > 
> > > There are architectures (32-bit ARM) where the kernel is mapped using
> > > section mappings, and we don't expect the Linux page table walking to
> > > work for section mappings.
> > 
> > This test doesn't go so far as to insert the PTE/PMD/PUD/... into the
> > page tables.  It merely needs an appropriately aligned PFN to create a
> > PTE/PMD/PUD/... from.
> 
> Well, in any case,
> 
> c085ac68 t kernel_init
> 
> so I'm not sure that would be an improvement.

I said "the corresponding pte/pmd/pud/p4d/pgd that encompasses that address"

So for a PTE, you'd use PFN 0xc085a000, for a PMD, you'd use PFN 0xc0000000
and for a PGD, you'd use PFN 0 (assuming 9 bits per level of table).


  reply	other threads:[~2019-07-25 22:57 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 " 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 [this message]
2019-07-26  4:47     ` Anshuman Khandual
2019-07-26 19:54       ` Matthew Wilcox
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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