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    SubjectRe: [PATCH v9 07/18] arm64: trans_pgd: hibernate: idmap the single page that holds the copy page routines
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    Hi Pavel,

    On 26/03/2020 03:24, Pavel Tatashin wrote:
    > From: James Morse <james.morse@arm.com>
    >
    > To resume from hibernate, the contents of memory are restored from
    > the swap image. This may overwrite any page, including the running
    > kernel and its page tables.
    >
    > Hibernate copies the code it uses to do the restore into a single
    > page that it knows won't be overwritten, and maps it with page tables
    > built from pages that won't be overwritten.
    >
    > Today the address it uses for this mapping is arbitrary, but to allow
    > kexec to reuse this code, it needs to be idmapped. To idmap the page
    > we must avoid the kernel helpers that have VA_BITS baked in.
    >
    > Convert create_single_mapping() to take a single PA, and idmap it.
    > The page tables are built in the reverse order to normal using
    > pfn_pte() to stir in any bits between 52:48. T0SZ is always increased
    > to cover 48bits, or 52 if the copy code has bits 52:48 in its PA.
    >
    > Pasha: The original patch from James
    > inux-arm-kernel/20200115143322.214247-4-james.morse@arm.com

    -EBROKENLINK

    The convention is to use a 'Link:' tag in the signed-off area.
    e.g. 5a3577039cbe

    > Adopted it to trans_pgd, so it can be commonly used by both Kexec
    > and Hibernate. Some minor clean-ups.

    Please describe your changes just before your SoB. This means each author sign's off on
    the stuff above their SoB, and its obvious who made which changes.

    Search for 'Lucky K Maintainer' in process/submitting-patches.rst for an example.


    > diff --git a/arch/arm64/include/asm/trans_pgd.h b/arch/arm64/include/asm/trans_pgd.h
    > index 97a7ea73b289..4912d3caf0ca 100644
    > --- a/arch/arm64/include/asm/trans_pgd.h
    > +++ b/arch/arm64/include/asm/trans_pgd.h
    > @@ -32,4 +32,7 @@ int trans_pgd_create_copy(struct trans_pgd_info *info, pgd_t **trans_pgd,
    > int trans_pgd_map_page(struct trans_pgd_info *info, pgd_t *trans_pgd,
    > void *page, unsigned long dst_addr, pgprot_t pgprot);

    This trans_pgd_map_page() used to be create_single_mapping(), which is where the original
    patch made its changes.

    You should only need one of these, not both.


    > +int trans_pgd_idmap_page(struct trans_pgd_info *info, phys_addr_t *trans_ttbr0,
    > + unsigned long *t0sz, void *page);
    > +
    > #endif /* _ASM_TRANS_TABLE_H */

    > diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
    > index 37d7d1c60f65..c2517d1af2af 100644
    > --- a/arch/arm64/mm/trans_pgd.c
    > +++ b/arch/arm64/mm/trans_pgd.c
    > @@ -242,3 +242,52 @@ int trans_pgd_map_page(struct trans_pgd_info *info, pgd_t *trans_pgd,
    >
    > return 0;
    > }
    > +
    > +/*
    > + * The page we want to idmap may be outside the range covered by VA_BITS that
    > + * can be built using the kernel's p?d_populate() helpers. As a one off, for a
    > + * single page, we build these page tables bottom up and just assume that will
    > + * need the maximum T0SZ.
    > + *
    > + * Returns 0 on success, and -ENOMEM on failure.
    > + * On success trans_ttbr0 contains page table with idmapped page, t0sz is set to

    > + * maxumum T0SZ for this page.

    maxumum

    > + */


    Thanks,

    James

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