KVM: PPC: Enable lightweight exits again

The PowerPC C ABI defines that registers r14-r31 need to be preserved across
function calls. Since our exit handler is written in C, we can make use of that
and don't need to reload r14-r31 on every entry/exit cycle.

This technique is also used in the BookE code and is called "lightweight exits"
there. To follow the tradition, it's called the same in Book3S.

So far this optimization was disabled though, as the code didn't do what it was
expected to do, but failed to work.

This patch fixes and enables lightweight exits again.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

2 files changed, 57 insertions, 53 deletions

diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index 492dcc198dd3..fd2a4d531582 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -539,8 +539,6 @@ int kvmppc_handle_pagefault(struct kvm_run *run, struct kvm_vcpu *vcpu,
                 r = kvmppc_emulate_mmio(run, vcpu);
                 if ( r == RESUME_HOST_NV )
                         r = RESUME_HOST;
-                if ( r == RESUME_GUEST_NV )
-                        r = RESUME_GUEST;
         }
 
         return r;
@@ -645,7 +643,7 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
                 er = kvmppc_emulate_instruction(run, vcpu);
                 switch (er) {
                 case EMULATE_DONE:
-                        r = RESUME_GUEST;
+                        r = RESUME_GUEST_NV;
                         break;
                 case EMULATE_FAIL:
                         printk(KERN_CRIT "%s: emulation at %lx failed (%08x)\n",
diff --git a/arch/powerpc/kvm/book3s_64_interrupts.S b/arch/powerpc/kvm/book3s_64_interrupts.S
index 7b55d8094c8b..d95d0d967d56 100644
--- a/arch/powerpc/kvm/book3s_64_interrupts.S
+++ b/arch/powerpc/kvm/book3s_64_interrupts.S
@@ -40,6 +40,26 @@
        mtmsrd  r0,1
 .endm
 
+#define VCPU_LOAD_NVGPRS(vcpu) \
+        ld      r14, VCPU_GPR(r14)(vcpu); \
+        ld      r15, VCPU_GPR(r15)(vcpu); \
+        ld      r16, VCPU_GPR(r16)(vcpu); \
+        ld      r17, VCPU_GPR(r17)(vcpu); \
+        ld      r18, VCPU_GPR(r18)(vcpu); \
+        ld      r19, VCPU_GPR(r19)(vcpu); \
+        ld      r20, VCPU_GPR(r20)(vcpu); \
+        ld      r21, VCPU_GPR(r21)(vcpu); \
+        ld      r22, VCPU_GPR(r22)(vcpu); \
+        ld      r23, VCPU_GPR(r23)(vcpu); \
+        ld      r24, VCPU_GPR(r24)(vcpu); \
+        ld      r25, VCPU_GPR(r25)(vcpu); \
+        ld      r26, VCPU_GPR(r26)(vcpu); \
+        ld      r27, VCPU_GPR(r27)(vcpu); \
+        ld      r28, VCPU_GPR(r28)(vcpu); \
+        ld      r29, VCPU_GPR(r29)(vcpu); \
+        ld      r30, VCPU_GPR(r30)(vcpu); \
+        ld      r31, VCPU_GPR(r31)(vcpu); \
+
 /*****************************************************************************
  *                                                                           *
  *     Guest entry / exit code that is in kernel module memory (highmem)     *
@@ -67,12 +87,16 @@ kvm_start_entry:
         SAVE_NVGPRS(r1)
 
         /* Save LR */
-        mflr    r14
-        std     r14, _LINK(r1)
+        std     r0, _LINK(r1)
+
+        /* Load non-volatile guest state from the vcpu */
+        VCPU_LOAD_NVGPRS(r4)
 
-/* XXX optimize non-volatile loading away */
 kvm_start_lightweight:
 
+        ld      r9, VCPU_PC(r4)                 /* r9 = vcpu->arch.pc */
+        ld      r10, VCPU_SHADOW_MSR(r4)        /* r10 = vcpu->arch.shadow_msr */
+
         DISABLE_INTERRUPTS
 
         /* Save R1/R2 in the PACA */
@@ -81,29 +105,6 @@ kvm_start_lightweight:
         ld      r3, VCPU_HIGHMEM_HANDLER(r4)
         std     r3, PACASAVEDMSR(r13)
 
-        /* Load non-volatile guest state from the vcpu */
-        ld      r14, VCPU_GPR(r14)(r4)
-        ld      r15, VCPU_GPR(r15)(r4)
-        ld      r16, VCPU_GPR(r16)(r4)
-        ld      r17, VCPU_GPR(r17)(r4)
-        ld      r18, VCPU_GPR(r18)(r4)
-        ld      r19, VCPU_GPR(r19)(r4)
-        ld      r20, VCPU_GPR(r20)(r4)
-        ld      r21, VCPU_GPR(r21)(r4)
-        ld      r22, VCPU_GPR(r22)(r4)
-        ld      r23, VCPU_GPR(r23)(r4)
-        ld      r24, VCPU_GPR(r24)(r4)
-        ld      r25, VCPU_GPR(r25)(r4)
-        ld      r26, VCPU_GPR(r26)(r4)
-        ld      r27, VCPU_GPR(r27)(r4)
-        ld      r28, VCPU_GPR(r28)(r4)
-        ld      r29, VCPU_GPR(r29)(r4)
-        ld      r30, VCPU_GPR(r30)(r4)
-        ld      r31, VCPU_GPR(r31)(r4)
-
-        ld      r9, VCPU_PC(r4)                 /* r9 = vcpu->arch.pc */
-        ld      r10, VCPU_SHADOW_MSR(r4)        /* r10 = vcpu->arch.shadow_msr */
-
         ld      r3, VCPU_TRAMPOLINE_ENTER(r4)
         mtsrr0  r3
 
@@ -247,7 +248,6 @@ kvmppc_handler_highmem:
 
 no_dcbz32_off:
 
-        /* XXX maybe skip on lightweight? */
         std     r14, VCPU_GPR(r14)(r12)
         std     r15, VCPU_GPR(r15)(r12)
         std     r16, VCPU_GPR(r16)(r12)
@@ -267,9 +267,6 @@ no_dcbz32_off:
         std     r30, VCPU_GPR(r30)(r12)
         std     r31, VCPU_GPR(r31)(r12)
 
-        /* Restore non-volatile host registers (r14 - r31) */
-        REST_NVGPRS(r1)
-
         /* Save guest PC (R10) */
         std     r10, VCPU_PC(r12)
 
@@ -351,42 +348,51 @@ kvm_return_point:
 
         /* Jump back to lightweight entry if we're supposed to */
         /* go back into the guest */
+
+        /* Pass the exit number as 3rd argument to kvmppc_handle_exit */
         mr      r5, r3
+
         /* Restore r3 (kvm_run) and r4 (vcpu) */
         REST_2GPRS(3, r1)
         bl      KVMPPC_HANDLE_EXIT
 
-#if 0 /* XXX get lightweight exits back */
+        /* If RESUME_GUEST, get back in the loop */
         cmpwi   r3, RESUME_GUEST
-        bne     kvm_exit_heavyweight
+        beq     kvm_loop_lightweight
 
-        /* put VCPU and KVM_RUN back into place and roll again! */
-        REST_2GPRS(3, r1)
-        b       kvm_start_lightweight
+        cmpwi   r3, RESUME_GUEST_NV
+        beq     kvm_loop_heavyweight
 
-kvm_exit_heavyweight:
-        /* Restore non-volatile host registers */
-        ld      r14, _LINK(r1)
-        mtlr    r14
-        REST_NVGPRS(r1)
+kvm_exit_loop:
 
-        addi    r1, r1, SWITCH_FRAME_SIZE
-#else
         ld      r4, _LINK(r1)
         mtlr    r4
 
-        cmpwi   r3, RESUME_GUEST
-        bne     kvm_exit_heavyweight
+        /* Restore non-volatile host registers (r14 - r31) */
+        REST_NVGPRS(r1)
+
+        addi    r1, r1, SWITCH_FRAME_SIZE
+        blr
+
+kvm_loop_heavyweight:
 
+        ld      r4, _LINK(r1)
+        std     r4, (16 + SWITCH_FRAME_SIZE)(r1)
+
+        /* Load vcpu and cpu_run */
         REST_2GPRS(3, r1)
 
-        addi    r1, r1, SWITCH_FRAME_SIZE
+        /* Load non-volatile guest state from the vcpu */
+        VCPU_LOAD_NVGPRS(r4)
 
-        b       kvm_start_entry
+        /* Jump back into the beginning of this function */
+        b       kvm_start_lightweight
 
-kvm_exit_heavyweight:
+kvm_loop_lightweight:
 
-        addi    r1, r1, SWITCH_FRAME_SIZE
-#endif
+        /* We'll need the vcpu pointer */
+        REST_GPR(4, r1)
+
+        /* Jump back into the beginning of this function */
+        b       kvm_start_lightweight
 
-        blr