linux-kernel - Re: [PATCH V14] mm/debug: Add tests validating architecture page table helpers

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Date:   Wed, 26 Feb 2020 15:44:23 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Qian Cai <cai@....pw>,
        Anshuman Khandual <anshuman.khandual@....com>,
        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
Subject: Re: [PATCH V14] mm/debug: Add tests validating architecture page
 table helpers



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 ?

Christophe