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    Subject[PATCH 5.15 028/913] iommu/iova: Improve 32-bit free space estimate
    Date
    From: Robin Murphy <robin.murphy@arm.com>

    commit 5b61343b50590fb04a3f6be2cdc4868091757262 upstream.

    For various reasons based on the allocator behaviour and typical
    use-cases at the time, when the max32_alloc_size optimisation was
    introduced it seemed reasonable to couple the reset of the tracked
    size to the update of cached32_node upon freeing a relevant IOVA.
    However, since subsequent optimisations focused on helping genuine
    32-bit devices make best use of even more limited address spaces, it
    is now a lot more likely for cached32_node to be anywhere in a "full"
    32-bit address space, and as such more likely for space to become
    available from IOVAs below that node being freed.

    At this point, the short-cut in __cached_rbnode_delete_update() really
    doesn't hold up any more, and we need to fix the logic to reliably
    provide the expected behaviour. We still want cached32_node to only move
    upwards, but we should reset the allocation size if *any* 32-bit space
    has become available.

    Reported-by: Yunfei Wang <yf.wang@mediatek.com>
    Signed-off-by: Robin Murphy <robin.murphy@arm.com>
    Reviewed-by: Miles Chen <miles.chen@mediatek.com>
    Link: https://lore.kernel.org/r/033815732d83ca73b13c11485ac39336f15c3b40.1646318408.git.robin.murphy@arm.com
    Signed-off-by: Joerg Roedel <jroedel@suse.de>
    Cc: Miles Chen <miles.chen@mediatek.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/iommu/iova.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    --- a/drivers/iommu/iova.c
    +++ b/drivers/iommu/iova.c
    @@ -154,10 +154,11 @@ __cached_rbnode_delete_update(struct iov
    cached_iova = to_iova(iovad->cached32_node);
    if (free == cached_iova ||
    (free->pfn_hi < iovad->dma_32bit_pfn &&
    - free->pfn_lo >= cached_iova->pfn_lo)) {
    + free->pfn_lo >= cached_iova->pfn_lo))
    iovad->cached32_node = rb_next(&free->node);
    +
    + if (free->pfn_lo < iovad->dma_32bit_pfn)
    iovad->max32_alloc_size = iovad->dma_32bit_pfn;
    - }

    cached_iova = to_iova(iovad->cached_node);
    if (free->pfn_lo >= cached_iova->pfn_lo)

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