arm64: KVM: Add SMCCC_ARCH_WORKAROUND_1 fast handling

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>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files 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