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

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Message-ID: <977b68ad-6796-4c3d-9c34-d023597f8ab2@amd.com>
Date: Thu, 6 Nov 2025 18:13:11 +0530
From: "Aithal, Srikanth" <sraithal@....com>
To: Heiko Carstens <hca@...ux.ibm.com>, Thomas Weißschuh
	<thomas.weissschuh@...utronix.de>
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 11/5/2025 9:04 PM, 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.

I was also hitting random hangs with an x86 KVM guest boot on an AMD64 
platform. The bisection landed on this commit as the culprit.
I see that v5 has been posted. I am in the process of testing that 
version and will reply to the v5 thread with the results.

Thank you
Srikanth Aithal <sraithal@....com>