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    SubjectRe: [PATCH v3 07/17] arm64, hibernate: move page handling function to new trans_pgd.c
    Date
    Hi Pavel,

    On 21/08/2019 19:31, Pavel Tatashin wrote:
    > Now, that we abstracted the required functions move them to a new home.
    > Later, we will generalize these function in order to be useful outside
    > of hibernation.

    > diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
    > new file mode 100644
    > index 000000000000..00b62d8640c2
    > --- /dev/null
    > +++ b/arch/arm64/mm/trans_pgd.c
    > @@ -0,0 +1,211 @@
    > +// SPDX-License-Identifier: GPL-2.0
    > +
    > +/*
    > + * Copyright (c) 2019, Microsoft Corporation.
    > + * Pavel Tatashin <patatash@linux.microsoft.com>

    Hmmm, while line-count isn't a useful metric: this file contains 41% of the code that was
    in hibernate.c, but has stripped the substantial copyright-pedigree that the hibernate
    code had built up over the years.
    (counting lines identified by 'cloc' as code, not comments or blank)

    If you are copying or moving a non trivial quantity of code, you need to preserve the
    copyright. Something like 'Derived from the arm64 hibernate support which has:'....


    > + */
    > +
    > +/*
    > + * Transitional tables are used during system transferring from one world to
    > + * another: such as during hibernate restore, and kexec reboots. During these
    > + * phases one cannot rely on page table not being overwritten.

    I think you need to mention that hibernate and kexec are rewriting memory, and may
    overwrite the live page tables, therefore ...


    > + *
    > + */
    > +
    > +#include <asm/trans_pgd.h>
    > +#include <asm/pgalloc.h>
    > +#include <asm/pgtable.h>
    > +#include <linux/suspend.h>

    #include <linux/bug.h>
    #include <linux/mm.h>
    #include <linux/mmzone.h>


    > +static void _copy_pte(pte_t *dst_ptep, pte_t *src_ptep, unsigned long addr)
    > +{
    > + pte_t pte = READ_ONCE(*src_ptep);
    > +

    > + if (pte_valid(pte)) {

    > + /*
    > + * Resume will overwrite areas that may be marked
    > + * read only (code, rodata). Clear the RDONLY bit from
    > + * the temporary mappings we use during restore.
    > + */
    > + set_pte(dst_ptep, pte_mkwrite(pte));

    > + } else if (debug_pagealloc_enabled() && !pte_none(pte)) {

    > + /*
    > + * debug_pagealloc will removed the PTE_VALID bit if
    > + * the page isn't in use by the resume kernel. It may have
    > + * been in use by the original kernel, in which case we need
    > + * to put it back in our copy to do the restore.
    > + *
    > + * Before marking this entry valid, check the pfn should
    > + * be mapped.
    > + */

    > + BUG_ON(!pfn_valid(pte_pfn(pte)));


    Thanks,

    James

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