KVM: PPC: PV mtmsrd L=0 and mtmsr

There is also a form of mtmsr where all bits need to be addressed. While the
PPC64 Linux kernel behaves resonably well here, on PPC32 we do not have an
L=1 form. It does mtmsr even for simple things like only changing EE.

So we need to hook into that one as well and check for a mask of bits that we
deem safe to change from within guest context.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

2 files changed, 135 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/kvm.c b/arch/powerpc/kernel/kvm.c
index 717ab0dded25..8ac57e2c52fa 100644
--- a/arch/powerpc/kernel/kvm.c
+++ b/arch/powerpc/kernel/kvm.c
@@ -63,7 +63,9 @@
 #define KVM_INST_MTSPR_DSISR    0x7c1203a6
 
 #define KVM_INST_TLBSYNC        0x7c00046c
+#define KVM_INST_MTMSRD_L0      0x7c000164
 #define KVM_INST_MTMSRD_L1      0x7c010164
+#define KVM_INST_MTMSR          0x7c000124
 
 static bool kvm_patching_worked = true;
 static char kvm_tmp[1024 * 1024];
@@ -176,6 +178,49 @@ static void kvm_patch_ins_mtmsrd(u32 *inst, u32 rt)
         kvm_patch_ins_b(inst, distance_start);
 }
 
+extern u32 kvm_emulate_mtmsr_branch_offs;
+extern u32 kvm_emulate_mtmsr_reg1_offs;
+extern u32 kvm_emulate_mtmsr_reg2_offs;
+extern u32 kvm_emulate_mtmsr_reg3_offs;
+extern u32 kvm_emulate_mtmsr_orig_ins_offs;
+extern u32 kvm_emulate_mtmsr_len;
+extern u32 kvm_emulate_mtmsr[];
+
+static void kvm_patch_ins_mtmsr(u32 *inst, u32 rt)
+{
+        u32 *p;
+        int distance_start;
+        int distance_end;
+        ulong next_inst;
+
+        p = kvm_alloc(kvm_emulate_mtmsr_len * 4);
+        if (!p)
+                return;
+
+        /* Find out where we are and put everything there */
+        distance_start = (ulong)p - (ulong)inst;
+        next_inst = ((ulong)inst + 4);
+        distance_end = next_inst - (ulong)&p[kvm_emulate_mtmsr_branch_offs];
+
+        /* Make sure we only write valid b instructions */
+        if (distance_start > KVM_INST_B_MAX) {
+                kvm_patching_worked = false;
+                return;
+        }
+
+        /* Modify the chunk to fit the invocation */
+        memcpy(p, kvm_emulate_mtmsr, kvm_emulate_mtmsr_len * 4);
+        p[kvm_emulate_mtmsr_branch_offs] |= distance_end & KVM_INST_B_MASK;
+        p[kvm_emulate_mtmsr_reg1_offs] |= rt;
+        p[kvm_emulate_mtmsr_reg2_offs] |= rt;
+        p[kvm_emulate_mtmsr_reg3_offs] |= rt;
+        p[kvm_emulate_mtmsr_orig_ins_offs] = *inst;
+        flush_icache_range((ulong)p, (ulong)p + kvm_emulate_mtmsr_len * 4);
+
+        /* Patch the invocation */
+        kvm_patch_ins_b(inst, distance_start);
+}
+
 static void kvm_map_magic_page(void *data)
 {
         kvm_hypercall2(KVM_HC_PPC_MAP_MAGIC_PAGE,
@@ -256,6 +301,12 @@ static void kvm_check_ins(u32 *inst)
                 if (get_rt(inst_rt) < 30)
                         kvm_patch_ins_mtmsrd(inst, inst_rt);
                 break;
+        case KVM_INST_MTMSR:
+        case KVM_INST_MTMSRD_L0:
+                /* We use r30 and r31 during the hook */
+                if (get_rt(inst_rt) < 30)
+                        kvm_patch_ins_mtmsr(inst, inst_rt);
+                break;
         }
 
         switch (_inst) {
diff --git a/arch/powerpc/kernel/kvm_emul.S b/arch/powerpc/kernel/kvm_emul.S
index 10dc4a6632fd..8cd22f47dd01 100644
--- a/arch/powerpc/kernel/kvm_emul.S
+++ b/arch/powerpc/kernel/kvm_emul.S
@@ -120,3 +120,87 @@ kvm_emulate_mtmsrd_reg_offs:
 .global kvm_emulate_mtmsrd_len
 kvm_emulate_mtmsrd_len:
         .long (kvm_emulate_mtmsrd_end - kvm_emulate_mtmsrd) / 4
+
+
+#define MSR_SAFE_BITS (MSR_EE | MSR_CE | MSR_ME | MSR_RI)
+#define MSR_CRITICAL_BITS ~MSR_SAFE_BITS
+
+.global kvm_emulate_mtmsr
+kvm_emulate_mtmsr:
+
+        SCRATCH_SAVE
+
+        /* Fetch old MSR in r31 */
+        LL64(r31, KVM_MAGIC_PAGE + KVM_MAGIC_MSR, 0)
+
+        /* Find the changed bits between old and new MSR */
+kvm_emulate_mtmsr_reg1:
+        xor     r31, r0, r31
+
+        /* Check if we need to really do mtmsr */
+        LOAD_REG_IMMEDIATE(r30, MSR_CRITICAL_BITS)
+        and.    r31, r31, r30
+
+        /* No critical bits changed? Maybe we can stay in the guest. */
+        beq     maybe_stay_in_guest
+
+do_mtmsr:
+
+        SCRATCH_RESTORE
+
+        /* Just fire off the mtmsr if it's critical */
+kvm_emulate_mtmsr_orig_ins:
+        mtmsr   r0
+
+        b       kvm_emulate_mtmsr_branch
+
+maybe_stay_in_guest:
+
+        /* Check if we have to fetch an interrupt */
+        lwz     r31, (KVM_MAGIC_PAGE + KVM_MAGIC_INT)(0)
+        cmpwi   r31, 0
+        beq+    no_mtmsr
+
+        /* Check if we may trigger an interrupt */
+kvm_emulate_mtmsr_reg2:
+        andi.   r31, r0, MSR_EE
+        beq     no_mtmsr
+
+        b       do_mtmsr
+
+no_mtmsr:
+
+        /* Put MSR into magic page because we don't call mtmsr */
+kvm_emulate_mtmsr_reg3:
+        STL64(r0, KVM_MAGIC_PAGE + KVM_MAGIC_MSR, 0)
+
+        SCRATCH_RESTORE
+
+        /* Go back to caller */
+kvm_emulate_mtmsr_branch:
+        b       .
+kvm_emulate_mtmsr_end:
+
+.global kvm_emulate_mtmsr_branch_offs
+kvm_emulate_mtmsr_branch_offs:
+        .long (kvm_emulate_mtmsr_branch - kvm_emulate_mtmsr) / 4
+
+.global kvm_emulate_mtmsr_reg1_offs
+kvm_emulate_mtmsr_reg1_offs:
+        .long (kvm_emulate_mtmsr_reg1 - kvm_emulate_mtmsr) / 4
+
+.global kvm_emulate_mtmsr_reg2_offs
+kvm_emulate_mtmsr_reg2_offs:
+        .long (kvm_emulate_mtmsr_reg2 - kvm_emulate_mtmsr) / 4
+
+.global kvm_emulate_mtmsr_reg3_offs
+kvm_emulate_mtmsr_reg3_offs:
+        .long (kvm_emulate_mtmsr_reg3 - kvm_emulate_mtmsr) / 4
+
+.global kvm_emulate_mtmsr_orig_ins_offs
+kvm_emulate_mtmsr_orig_ins_offs:
+        .long (kvm_emulate_mtmsr_orig_ins - kvm_emulate_mtmsr) / 4
+
+.global kvm_emulate_mtmsr_len
+kvm_emulate_mtmsr_len:
+        .long (kvm_emulate_mtmsr_end - kvm_emulate_mtmsr) / 4