arm64: KVM: Optimize __guest_enter/exit() to save a few instructions

We are doing an unnecessary stack push/pop operation when restoring
the guest registers x0-x18 in __guest_enter(). This patch saves the
two instructions by using x18 as a base register. No need to store
the vcpu context pointer in stack because it is redundant, the same
information is available in tpidr_el2. The function __guest_exit()
calling convention is slightly modified, caller only pushes the regs
x0-x1 to stack instead of regs x0-x3.

Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index ce9e5e5..3967c23 100644 (file)
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -55,79 +55,78 @@
  */
 ENTRY(__guest_enter)
        // x0: vcpu
-       // x1: host/guest context
-       // x2-x18: clobbered by macros
+       // x1: host context
+       // x2-x17: clobbered by macros
+       // x18: guest context
 
        // Store the host regs
        save_callee_saved_regs x1
 
-       // Preserve vcpu & host_ctxt for use at exit time
-       stp     x0, x1, [sp, #-16]!
+       // Store the host_ctxt for use at exit time
+       str     x1, [sp, #-16]!
 
-       add     x1, x0, #VCPU_CONTEXT
+       add     x18, x0, #VCPU_CONTEXT
 
-       // Prepare x0-x1 for later restore by pushing them onto the stack
-       ldp     x2, x3, [x1, #CPU_XREG_OFFSET(0)]
-       stp     x2, x3, [sp, #-16]!
+       // Restore guest regs x0-x17
+       ldp     x0, x1,   [x18, #CPU_XREG_OFFSET(0)]
+       ldp     x2, x3,   [x18, #CPU_XREG_OFFSET(2)]
+       ldp     x4, x5,   [x18, #CPU_XREG_OFFSET(4)]
+       ldp     x6, x7,   [x18, #CPU_XREG_OFFSET(6)]
+       ldp     x8, x9,   [x18, #CPU_XREG_OFFSET(8)]
+       ldp     x10, x11, [x18, #CPU_XREG_OFFSET(10)]
+       ldp     x12, x13, [x18, #CPU_XREG_OFFSET(12)]
+       ldp     x14, x15, [x18, #CPU_XREG_OFFSET(14)]
+       ldp     x16, x17, [x18, #CPU_XREG_OFFSET(16)]
 
-       // x2-x18
-       ldp     x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
-       ldp     x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
-       ldp     x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
-       ldp     x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
-       ldp     x10, x11, [x1, #CPU_XREG_OFFSET(10)]
-       ldp     x12, x13, [x1, #CPU_XREG_OFFSET(12)]
-       ldp     x14, x15, [x1, #CPU_XREG_OFFSET(14)]
-       ldp     x16, x17, [x1, #CPU_XREG_OFFSET(16)]
-       ldr     x18,      [x1, #CPU_XREG_OFFSET(18)]
-
-       // x19-x29, lr
-       restore_callee_saved_regs x1
-
-       // Last bits of the 64bit state
-       ldp     x0, x1, [sp], #16
+       // Restore guest regs x19-x29, lr
+       restore_callee_saved_regs x18
+
+       // Restore guest reg x18
+       ldr     x18,      [x18, #CPU_XREG_OFFSET(18)]
 
        // Do not touch any register after this!
        eret
 ENDPROC(__guest_enter)
 
 ENTRY(__guest_exit)
-       // x0: vcpu
-       // x1: return code
-       // x2-x3: free
-       // x4-x29,lr: vcpu regs
-       // vcpu x0-x3 on the stack
-
-       add     x2, x0, #VCPU_CONTEXT
-
-       stp     x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
-       stp     x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
-       stp     x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
-       stp     x10, x11, [x2, #CPU_XREG_OFFSET(10)]
-       stp     x12, x13, [x2, #CPU_XREG_OFFSET(12)]
-       stp     x14, x15, [x2, #CPU_XREG_OFFSET(14)]
-       stp     x16, x17, [x2, #CPU_XREG_OFFSET(16)]
-       str     x18,      [x2, #CPU_XREG_OFFSET(18)]
-
-       ldp     x6, x7, [sp], #16       // x2, x3
-       ldp     x4, x5, [sp], #16       // x0, x1
-
-       stp     x4, x5, [x2, #CPU_XREG_OFFSET(0)]
-       stp     x6, x7, [x2, #CPU_XREG_OFFSET(2)]
+       // x0: return code
+       // x1: vcpu
+       // x2-x29,lr: vcpu regs
+       // vcpu x0-x1 on the stack
+
+       add     x1, x1, #VCPU_CONTEXT
+
+       // Store the guest regs x2 and x3
+       stp     x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
+
+       // Retrieve the guest regs x0-x1 from the stack
+       ldp     x2, x3, [sp], #16       // x0, x1
+
+       // Store the guest regs x0-x1 and x4-x18
+       stp     x2, x3,   [x1, #CPU_XREG_OFFSET(0)]
+       stp     x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
+       stp     x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
+       stp     x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
+       stp     x10, x11, [x1, #CPU_XREG_OFFSET(10)]
+       stp     x12, x13, [x1, #CPU_XREG_OFFSET(12)]
+       stp     x14, x15, [x1, #CPU_XREG_OFFSET(14)]
+       stp     x16, x17, [x1, #CPU_XREG_OFFSET(16)]
+       str     x18,      [x1, #CPU_XREG_OFFSET(18)]
+
+       // Store the guest regs x19-x29, lr
+       save_callee_saved_regs x1
 
-       save_callee_saved_regs x2
+       // Restore the host_ctxt from the stack
+       ldr     x2, [sp], #16
 
-       // Restore vcpu & host_ctxt from the stack
-       // (preserving return code in x1)
-       ldp     x0, x2, [sp], #16
        // Now restore the host regs
        restore_callee_saved_regs x2
 
-       mov     x0, x1
        ret
 ENDPROC(__guest_exit)
 
 ENTRY(__fpsimd_guest_restore)
+       stp     x2, x3, [sp, #-16]!
        stp     x4, lr, [sp, #-16]!
 
 alternative_if_not ARM64_HAS_VIRT_HOST_EXTN

diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index f6d9694..d6cae54 100644 (file)
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -27,16 +27,6 @@
        .text
        .pushsection    .hyp.text, "ax"
 
-.macro save_x0_to_x3
-       stp     x0, x1, [sp, #-16]!
-       stp     x2, x3, [sp, #-16]!
-.endm
-
-.macro restore_x0_to_x3
-       ldp     x2, x3, [sp], #16
-       ldp     x0, x1, [sp], #16
-.endm
-
 .macro do_el2_call
        /*
         * Shuffle the parameters before calling the function
@@ -79,23 +69,23 @@ ENTRY(__kvm_hyp_teardown)
 ENDPROC(__kvm_hyp_teardown)
        
 el1_sync:                              // Guest trapped into EL2
-       save_x0_to_x3
+       stp     x0, x1, [sp, #-16]!
 
 alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
        mrs     x1, esr_el2
 alternative_else
        mrs     x1, esr_el1
 alternative_endif
-       lsr     x2, x1, #ESR_ELx_EC_SHIFT
+       lsr     x0, x1, #ESR_ELx_EC_SHIFT
 
-       cmp     x2, #ESR_ELx_EC_HVC64
+       cmp     x0, #ESR_ELx_EC_HVC64
        b.ne    el1_trap
 
-       mrs     x3, vttbr_el2           // If vttbr is valid, the 64bit guest
-       cbnz    x3, el1_trap            // called HVC
+       mrs     x1, vttbr_el2           // If vttbr is valid, the 64bit guest
+       cbnz    x1, el1_trap            // called HVC
 
        /* Here, we're pretty sure the host called HVC. */
-       restore_x0_to_x3
+       ldp     x0, x1, [sp], #16
 
        cmp     x0, #HVC_GET_VECTORS
        b.ne    1f
@@ -113,22 +103,21 @@ alternative_endif
 
 el1_trap:
        /*
-        * x1: ESR
-        * x2: ESR_EC
+        * x0: ESR_EC
         */
 
        /* Guest accessed VFP/SIMD registers, save host, restore Guest */
-       cmp     x2, #ESR_ELx_EC_FP_ASIMD
+       cmp     x0, #ESR_ELx_EC_FP_ASIMD
        b.eq    __fpsimd_guest_restore
 
-       mrs     x0, tpidr_el2
-       mov     x1, #ARM_EXCEPTION_TRAP
+       mrs     x1, tpidr_el2
+       mov     x0, #ARM_EXCEPTION_TRAP
        b       __guest_exit
 
 el1_irq:
-       save_x0_to_x3
-       mrs     x0, tpidr_el2
-       mov     x1, #ARM_EXCEPTION_IRQ
+       stp     x0, x1, [sp, #-16]!
+       mrs     x1, tpidr_el2
+       mov     x0, #ARM_EXCEPTION_IRQ
        b       __guest_exit
 
 ENTRY(__hyp_do_panic)