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    Subject[PATCH v2 7/7] KVM: arm64: Use less bits for hyp_page refcount
    From
    The hyp_page refcount is currently encoded on 4 bytes even though we
    never need to count that many objects in a page. Make it 2 bytes to save
    some space in the vmemmap.

    As overflows are more likely to happen as well, make sure to catch those
    with a BUG in the increment function.

    Signed-off-by: Quentin Perret <qperret@google.com>
    ---
    arch/arm64/kvm/hyp/include/nvhe/memory.h | 2 +-
    arch/arm64/kvm/hyp/nvhe/page_alloc.c | 1 +
    2 files changed, 2 insertions(+), 1 deletion(-)

    diff --git a/arch/arm64/kvm/hyp/include/nvhe/memory.h b/arch/arm64/kvm/hyp/include/nvhe/memory.h
    index 3fe34fa30ea4..592b7edb3edb 100644
    --- a/arch/arm64/kvm/hyp/include/nvhe/memory.h
    +++ b/arch/arm64/kvm/hyp/include/nvhe/memory.h
    @@ -8,7 +8,7 @@
    #include <linux/types.h>

    struct hyp_page {
    - unsigned int refcount;
    + unsigned short refcount;
    unsigned short order;
    };

    diff --git a/arch/arm64/kvm/hyp/nvhe/page_alloc.c b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
    index be07055bbc10..41fc25bdfb34 100644
    --- a/arch/arm64/kvm/hyp/nvhe/page_alloc.c
    +++ b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
    @@ -146,6 +146,7 @@ static struct hyp_page *__hyp_extract_page(struct hyp_pool *pool,

    static inline void hyp_page_ref_inc(struct hyp_page *p)
    {
    + BUG_ON(p->refcount == USHRT_MAX);
    p->refcount++;
    }

    --
    2.32.0.rc0.204.g9fa02ecfa5-goog
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