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    Subject[PATCH v14 4/6] KVM: s390: pv: avoid export before import if possible
    Date
    If the appropriate UV feature bit is set, there is no need to perform
    an export before import.

    The misc feature indicates, among other things, that importing a shared
    page from a different protected VM will automatically also transfer its
    ownership.

    Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
    Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
    Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
    ---
    arch/s390/kernel/uv.c | 7 +++++++
    1 file changed, 7 insertions(+)

    diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
    index f9810d2a267c..9f18a4af9c13 100644
    --- a/arch/s390/kernel/uv.c
    +++ b/arch/s390/kernel/uv.c
    @@ -255,6 +255,13 @@ static int make_secure_pte(pte_t *ptep, unsigned long addr,
    */
    static bool should_export_before_import(struct uv_cb_header *uvcb, struct mm_struct *mm)
    {
    + /*
    + * The misc feature indicates, among other things, that importing a
    + * shared page from a different protected VM will automatically also
    + * transfer its ownership.
    + */
    + if (test_bit_inv(BIT_UV_FEAT_MISC, &uv_info.uv_feature_indications))
    + return false;
    if (uvcb->cmd == UVC_CMD_UNPIN_PAGE_SHARED)
    return false;
    return atomic_read(&mm->context.protected_count) > 1;
    --
    2.37.3
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