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    SubjectRe: [PATCH V14] mm/debug: Add tests validating architecture page table helpers
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    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@arm.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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