KVM: PPC: Book3S HV P9: Switch to guest MMU context as late as possible

Move MMU context switch as late as reasonably possible to minimise code
running with guest context switched in. This becomes more important when
this code may run in real-mode, with later changes.

Move WARN_ON as early as possible so program check interrupts are less
likely to tangle everything up.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210528090752.3542186-21-npiggin@gmail.com

diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index f24a126..0b5bd00 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -138,8 +138,13 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
        if (hdec < 0)
                return BOOK3S_INTERRUPT_HV_DECREMENTER;
 
+       WARN_ON_ONCE(vcpu->arch.shregs.msr & MSR_HV);
+       WARN_ON_ONCE(!(vcpu->arch.shregs.msr & MSR_ME));
+
        start_timing(vcpu, &vcpu->arch.rm_entry);
 
+       vcpu->arch.ceded = 0;
+
        if (vc->tb_offset) {
                u64 new_tb = mftb() + vc->tb_offset;
                mtspr(SPRN_TBU40, new_tb);
@@ -188,26 +193,6 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
 
        mtspr(SPRN_HFSCR, vcpu->arch.hfscr);
 
-       mtspr(SPRN_SPRG0, vcpu->arch.shregs.sprg0);
-       mtspr(SPRN_SPRG1, vcpu->arch.shregs.sprg1);
-       mtspr(SPRN_SPRG2, vcpu->arch.shregs.sprg2);
-       mtspr(SPRN_SPRG3, vcpu->arch.shregs.sprg3);
-
-       mtspr(SPRN_AMOR, ~0UL);
-
-       switch_mmu_to_guest_radix(kvm, vcpu, lpcr);
-
-       /*
-        * P9 suppresses the HDEC exception when LPCR[HDICE] = 0,
-        * so set guest LPCR (with HDICE) before writing HDEC.
-        */
-       mtspr(SPRN_HDEC, hdec);
-
-       vcpu->arch.ceded = 0;
-
-       WARN_ON_ONCE(vcpu->arch.shregs.msr & MSR_HV);
-       WARN_ON_ONCE(!(vcpu->arch.shregs.msr & MSR_ME));
-
        mtspr(SPRN_HSRR0, vcpu->arch.regs.nip);
        mtspr(SPRN_HSRR1, (vcpu->arch.shregs.msr & ~MSR_HV) | MSR_ME);
 
@@ -226,6 +211,21 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
         */
        mtspr(SPRN_HDSISR, HDSISR_CANARY);
 
+       mtspr(SPRN_SPRG0, vcpu->arch.shregs.sprg0);
+       mtspr(SPRN_SPRG1, vcpu->arch.shregs.sprg1);
+       mtspr(SPRN_SPRG2, vcpu->arch.shregs.sprg2);
+       mtspr(SPRN_SPRG3, vcpu->arch.shregs.sprg3);
+
+       mtspr(SPRN_AMOR, ~0UL);
+
+       switch_mmu_to_guest_radix(kvm, vcpu, lpcr);
+
+       /*
+        * P9 suppresses the HDEC exception when LPCR[HDICE] = 0,
+        * so set guest LPCR (with HDICE) before writing HDEC.
+        */
+       mtspr(SPRN_HDEC, hdec);
+
        __mtmsrd(0, 1); /* clear RI */
 
        mtspr(SPRN_DAR, vcpu->arch.shregs.dar);