linux-kernel - Re: [PATCH v4 24/35] vdso/datastore: Allocate data pages dynamically

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Message-ID: <20251105170813-070d53d9-aa2a-4cb6-bcda-3bce8c5be9c1@linutronix.de>
Date: Wed, 5 Nov 2025 17:13:49 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: Andy Lutomirski <luto@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Vincenzo Frascino <vincenzo.frascino@....com>, 
	Arnd Bergmann <arnd@...db.de>, "David S. Miller" <davem@...emloft.net>, 
	Andreas Larsson <andreas@...sler.com>, Nick Alcock <nick.alcock@...cle.com>, 
	John Stultz <jstultz@...gle.com>, Stephen Boyd <sboyd@...nel.org>, 
	John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>, Shuah Khan <shuah@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Theodore Ts'o <tytso@....edu>, 
	"Jason A. Donenfeld" <Jason@...c4.com>, Russell King <linux@...linux.org.uk>, 
	Madhavan Srinivasan <maddy@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>, 
	Nicholas Piggin <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>, 
	Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>, 
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>, Vasily Gorbik <gor@...ux.ibm.com>, 
	Alexander Gordeev <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Sven Schnelle <svens@...ux.ibm.com>, Nagarathnam Muthusamy <nagarathnam.muthusamy@...cle.com>, 
	Shannon Nelson <sln@...main.com>, linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linuxppc-dev@...ts.ozlabs.org, loongarch@...ts.linux.dev, linux-mips@...r.kernel.org, 
	linux-s390@...r.kernel.org
Subject: Re: [PATCH v4 24/35] vdso/datastore: Allocate data pages dynamically

On Wed, Nov 05, 2025 at 04:34:26PM +0100, Heiko Carstens wrote:
> On Tue, Oct 14, 2025 at 08:49:10AM +0200, Thomas Weißschuh wrote:
> > Allocating the datapages as part of the kernel image does not work on
> > SPARC. It is also problematic with regards to dcache aliasing as there is
> > no guarantee that the virtual addresses used by the kernel are compatible
> > with those used by userspace.
> > 
> > Allocate the data pages through the page allocator instead.
> > Unused pages in the vDSO VMA are still allocated to keep the virtual
> > addresses aligned.
> > 
> > These pages are used by both the timekeeping, random pool and architecture
> > initialization code. Introduce a new early initialization step, to make
> > sure they are available when needed.
> > 
> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> > Tested-by: Andreas Larsson <andreas@...sler.com>
> > Reviewed-by: Andreas Larsson <andreas@...sler.com>
> > ---
> >  include/linux/vdso_datastore.h |  6 ++++++
> >  init/main.c                    |  2 ++
> >  lib/vdso/datastore.c           | 44 ++++++++++++++++++++++--------------------
> >  3 files changed, 31 insertions(+), 21 deletions(-)
> 
> ...
> 
> > +void __init vdso_setup_data_pages(void)
> > +{
> > +	unsigned int order = get_order(VDSO_NR_PAGES * PAGE_SIZE);
> > +	struct folio *folio = folio_alloc(GFP_KERNEL, order);
> 
> I'm seeing random hangs on s390 too with our CI, but unfortunately I cannot
> reproduce it manually. But looking at one of the dumps it looks to me like the
> vdso time page contains (more or less) random junk at the end. Or in other
> words, shouldn't this be:
> 
> 	struct folio *folio = folio_alloc(GFP_KERNEL | __GFP_ZERO, order);
> 
> ? At least that is a difference to before as far as I can tell.

Thanks! This perfectly explains all the weird issues. It also does fix
the issue on the affected hardware which Mark kindly let me use.
I'll test it some more and send a fixed series tomorrow.


Thanks again!
Thomas