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Message-ID: <52db1e9b-83b3-c41f-ef03-0f43e2159a83@arm.com>
Date: Thu, 27 Feb 2020 08:04:05 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Christophe Leroy <christophe.leroy@....fr>, Qian Cai <cai@....pw>,
linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Mike Rapoport <rppt@...ux.ibm.com>,
Vineet Gupta <vgupta@...opsys.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Michael Ellerman <mpe@...erman.id.au>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
"Kirill A . Shutemov" <kirill@...temov.name>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
linux-snps-arc@...ts.infradead.org,
linux-arm-kernel@...ts.infradead.org,
linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
linux-riscv@...ts.infradead.org, x86@...nel.org,
linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
James Morse <james.morse@....com>
Subject: Re: [PATCH V14] mm/debug: Add tests validating architecture page
table helpers
On 02/26/2020 08:14 PM, Christophe Leroy wrote:
>
>
> Le 26/02/2020 à 15:12, Qian Cai a écrit :
>> On Wed, 2020-02-26 at 09:09 -0500, Qian Cai wrote:
>>> On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote:
>>>
>>> How useful is this that straightly crash the powerpc?
>>
>> And then generate warnings on arm64,
>>
>> [ 146.634626][ T1] debug_vm_pgtable: debug_vm_pgtable: Validating
>> architecture page table helpers
>> [ 146.643995][ T1] ------------[ cut here ]------------
>> [ 146.649350][ T1] virt_to_phys used for non-linear address:
>> (____ptrval____) (start_kernel+0x0/0x580)
>
> Must be something wrong with the following in debug_vm_pgtable()
>
> paddr = __pa(&start_kernel);
>
> Is there any explaination why start_kernel() is not in linear memory on ARM64 ?
Cc: + James Morse <james.morse@....com>
This warning gets exposed with DEBUG_VIRTUAL due to __pa() on a kernel symbol
i.e 'start_kernel' which might be outside the linear map. This happens due to
kernel mapping position randomization with KASLR. Adding James here in case he
might like to add more.
__pa_symbol() should have been used instead, for accessing the physical address
here. On arm64 __pa() does check for linear address with __is_lm_address() and
switch accordingly if it is a kernel text symbol. Nevertheless, its much better
to use __pa_symbol() here rather than __pa().
Rather than respining the patch once more, will just send a fix replacing this
helper __pa() with __pa_symbol() for Andrew to pick up as this patch is already
part of linux-next (next-20200226). But can definitely respin if that will be
preferred.
Thanks Qian for catching this.
>
> Christophe
>
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