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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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