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    Subject[PATCH 5.10 011/101] arm64: Ignore any DMA offsets in the max_zone_phys() calculation
    Date
    From: Catalin Marinas <catalin.marinas@arm.com>

    commit 791ab8b2e3db0c6e4295467d10398800ec29144c upstream.

    Currently, the kernel assumes that if RAM starts above 32-bit (or
    zone_bits), there is still a ZONE_DMA/DMA32 at the bottom of the RAM and
    such constrained devices have a hardwired DMA offset. In practice, we
    haven't noticed any such hardware so let's assume that we can expand
    ZONE_DMA32 to the available memory if no RAM below 4GB. Similarly,
    ZONE_DMA is expanded to the 4GB limit if no RAM addressable by
    zone_bits.

    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
    Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
    Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
    Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
    Cc: Robin Murphy <robin.murphy@arm.com>
    Link: https://lore.kernel.org/r/20201118185809.1078362-1-catalin.marinas@arm.com
    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/arm64/mm/init.c | 17 ++++++++++++-----
    1 file changed, 12 insertions(+), 5 deletions(-)

    diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
    index a985d292e820..c0a7f0d90b39 100644
    --- a/arch/arm64/mm/init.c
    +++ b/arch/arm64/mm/init.c
    @@ -174,14 +174,21 @@ static void __init reserve_elfcorehdr(void)
    #endif /* CONFIG_CRASH_DUMP */

    /*
    - * Return the maximum physical address for a zone with a given address size
    - * limit. It currently assumes that for memory starting above 4G, 32-bit
    - * devices will use a DMA offset.
    + * Return the maximum physical address for a zone accessible by the given bits
    + * limit. If DRAM starts above 32-bit, expand the zone to the maximum
    + * available memory, otherwise cap it at 32-bit.
    */
    static phys_addr_t __init max_zone_phys(unsigned int zone_bits)
    {
    - phys_addr_t offset = memblock_start_of_DRAM() & GENMASK_ULL(63, zone_bits);
    - return min(offset + (1ULL << zone_bits), memblock_end_of_DRAM());
    + phys_addr_t zone_mask = DMA_BIT_MASK(zone_bits);
    + phys_addr_t phys_start = memblock_start_of_DRAM();
    +
    + if (phys_start > U32_MAX)
    + zone_mask = PHYS_ADDR_MAX;
    + else if (phys_start > zone_mask)
    + zone_mask = U32_MAX;
    +
    + return min(zone_mask, memblock_end_of_DRAM() - 1) + 1;
    }

    static void __init zone_sizes_init(unsigned long min, unsigned long max)
    --
    2.30.2
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