KVM: arm64: Avoid repetitive stack access on host EL1 to EL2 exception

Registers x0/x1 get repeateadly pushed and poped during a host
HVC call. Instead, leave the registers on the stack, trading
a store instruction on the fast path for an add on the slow path.

Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S
index 4e207c1c512674ca4152a4a7623d4003fdcd3e83..fe2740b224cf05b51e861b6c5bcffa3860cec7c8 100644 (file)
--- a/arch/arm64/kvm/hyp/nvhe/host.S
+++ b/arch/arm64/kvm/hyp/nvhe/host.S
@@ -13,8 +13,6 @@
        .text
 
 SYM_FUNC_START(__host_exit)
-       stp     x0, x1, [sp, #-16]!
-
        get_host_ctxt   x0, x1
 
        /* Store the host regs x2 and x3 */
@@ -99,13 +97,15 @@ SYM_FUNC_END(__hyp_do_panic)
        mrs     x0, esr_el2
        lsr     x0, x0, #ESR_ELx_EC_SHIFT
        cmp     x0, #ESR_ELx_EC_HVC64
-       ldp     x0, x1, [sp], #16
        b.ne    __host_exit
 
+       ldp     x0, x1, [sp]            // Don't fixup the stack yet
+
        /* Check for a stub HVC call */
        cmp     x0, #HVC_STUB_HCALL_NR
        b.hs    __host_exit
 
+       add     sp, sp, #16
        /*
         * Compute the idmap address of __kvm_handle_stub_hvc and
         * jump there. Since we use kimage_voffset, do not use the