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    Subject[PATCH v4 11/17] arm64: KVM: Add SMCCC_ARCH_WORKAROUND_1 fast handling
    Date
    We want SMCCC_ARCH_WORKAROUND_1 to be fast. As fast as possible.
    So let's intercept it as early as we can by testing for the
    function call number as soon as we've identified a HVC call
    coming from the guest.

    Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
    Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
    ---
    arch/arm64/kvm/hyp/hyp-entry.S | 20 ++++++++++++++++++--
    1 file changed, 18 insertions(+), 2 deletions(-)

    diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
    index e4f37b9dd47c..f36464bd57c5 100644
    --- a/arch/arm64/kvm/hyp/hyp-entry.S
    +++ b/arch/arm64/kvm/hyp/hyp-entry.S
    @@ -15,6 +15,7 @@
    * along with this program. If not, see <http://www.gnu.org/licenses/>.
    */

    +#include <linux/arm-smccc.h>
    #include <linux/linkage.h>

    #include <asm/alternative.h>
    @@ -64,10 +65,11 @@ alternative_endif
    lsr x0, x1, #ESR_ELx_EC_SHIFT

    cmp x0, #ESR_ELx_EC_HVC64
    + ccmp x0, #ESR_ELx_EC_HVC32, #4, ne
    b.ne el1_trap

    - mrs x1, vttbr_el2 // If vttbr is valid, the 64bit guest
    - cbnz x1, el1_trap // called HVC
    + mrs x1, vttbr_el2 // If vttbr is valid, the guest
    + cbnz x1, el1_hvc_guest // called HVC

    /* Here, we're pretty sure the host called HVC. */
    ldp x0, x1, [sp], #16
    @@ -100,6 +102,20 @@ alternative_endif

    eret

    +el1_hvc_guest:
    + /*
    + * Fastest possible path for ARM_SMCCC_ARCH_WORKAROUND_1.
    + * The workaround has already been applied on the host,
    + * so let's quickly get back to the guest. We don't bother
    + * restoring x1, as it can be clobbered anyway.
    + */
    + ldr x1, [sp] // Guest's x0
    + eor w1, w1, #ARM_SMCCC_ARCH_WORKAROUND_1
    + cbnz w1, el1_trap
    + mov x0, x1
    + add sp, sp, #16
    + eret
    +
    el1_trap:
    /*
    * x0: ESR_EC
    --
    2.14.2
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