[RFC PATCH 15/43] KVM: PPC: Book3S HV: CTRL SPR does not require read-modify-write

[Nicholas Piggin]

Processors that support KVM HV do not require read-modify-write of
the CTRL SPR to set/clear their thread's runlatch. Just write 1 or 0
to it.

Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
 arch/powerpc/kvm/book3s_hv.c            |  2 +-
 arch/powerpc/kvm/book3s_hv_rmhandlers.S | 15 ++++++---------
 2 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 0733bb95f439..f0298b286c42 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3920,7 +3920,7 @@ static void load_spr_state(struct kvm_vcpu *vcpu)
         */
 
        if (!(vcpu->arch.ctrl & 1))
-               mtspr(SPRN_CTRLT, mfspr(SPRN_CTRLF) & ~1);
+               mtspr(SPRN_CTRLT, 0);
 }
 
 static void store_spr_state(struct kvm_vcpu *vcpu)
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S 
b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 0eb06734bc26..488a1e07958c 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -775,12 +775,11 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
        mtspr   SPRN_AMR,r5
        mtspr   SPRN_UAMOR,r6
 
-       /* Restore state of CTRL run bit; assume 1 on entry */
+       /* Restore state of CTRL run bit; the host currently has it set to 1 */
        lwz     r5,VCPU_CTRL(r4)
        andi.   r5,r5,1
        bne     4f
-       mfspr   r6,SPRN_CTRLF
-       clrrdi  r6,r6,1
+       li      r6,0
        mtspr   SPRN_CTRLT,r6
 4:
        /* Secondary threads wait for primary to have done partition switch */
@@ -1209,12 +1208,12 @@ guest_bypass:
        stw     r0, VCPU_CPU(r9)
        stw     r0, VCPU_THREAD_CPU(r9)
 
-       /* Save guest CTRL register, set runlatch to 1 */
+       /* Save guest CTRL register, set runlatch to 1 if it was clear */
        mfspr   r6,SPRN_CTRLF
        stw     r6,VCPU_CTRL(r9)
        andi.   r0,r6,1
        bne     4f
-       ori     r6,r6,1
+       li      r6,1
        mtspr   SPRN_CTRLT,r6
 4:
        /*
@@ -2220,8 +2219,7 @@ END_FTR_SECTION_IFCLR(CPU_FTR_TM)
         * Also clear the runlatch bit before napping.
         */
 kvm_do_nap:
-       mfspr   r0, SPRN_CTRLF
-       clrrdi  r0, r0, 1
+       li      r0,0
        mtspr   SPRN_CTRLT, r0
 
        li      r0,1
@@ -2240,8 +2238,7 @@ kvm_nap_sequence:         /* desired LPCR value in r5 */
 
        bl      isa206_idle_insn_mayloss
 
-       mfspr   r0, SPRN_CTRLF
-       ori     r0, r0, 1
+       li      r0,1
        mtspr   SPRN_CTRLT, r0
 
        mtspr   SPRN_SRR1, r3
-- 
2.23.0