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    Subject[PATCH 5.10 140/563] arm64: clear_page() shouldnt use DC ZVA when DCZID_EL0.DZP == 1
    Date
    From: Reiji Watanabe <reijiw@google.com>

    [ Upstream commit f0616abd4e67143b45b04b565839148458857347 ]

    Currently, clear_page() uses DC ZVA instruction unconditionally. But it
    should make sure that DCZID_EL0.DZP, which indicates whether or not use
    of DC ZVA instruction is prohibited, is zero when using the instruction.
    Use STNP instead when DCZID_EL0.DZP == 1.

    Fixes: f27bb139c387 ("arm64: Miscellaneous library functions")
    Signed-off-by: Reiji Watanabe <reijiw@google.com>
    Reviewed-by: Robin Murphy <robin.murphy@arm.com>
    Link: https://lore.kernel.org/r/20211206004736.1520989-2-reijiw@google.com
    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/arm64/lib/clear_page.S | 10 ++++++++++
    1 file changed, 10 insertions(+)

    diff --git a/arch/arm64/lib/clear_page.S b/arch/arm64/lib/clear_page.S
    index b84b179edba3a..1fd5d790ab800 100644
    --- a/arch/arm64/lib/clear_page.S
    +++ b/arch/arm64/lib/clear_page.S
    @@ -16,6 +16,7 @@
    */
    SYM_FUNC_START_PI(clear_page)
    mrs x1, dczid_el0
    + tbnz x1, #4, 2f /* Branch if DC ZVA is prohibited */
    and w1, w1, #0xf
    mov x2, #4
    lsl x1, x2, x1
    @@ -25,5 +26,14 @@ SYM_FUNC_START_PI(clear_page)
    tst x0, #(PAGE_SIZE - 1)
    b.ne 1b
    ret
    +
    +2: stnp xzr, xzr, [x0]
    + stnp xzr, xzr, [x0, #16]
    + stnp xzr, xzr, [x0, #32]
    + stnp xzr, xzr, [x0, #48]
    + add x0, x0, #64
    + tst x0, #(PAGE_SIZE - 1)
    + b.ne 2b
    + ret
    SYM_FUNC_END_PI(clear_page)
    EXPORT_SYMBOL(clear_page)
    --
    2.34.1


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