[PATCH 24/27] KVM: PPC: PV mtmsrd L=1

Alexander Graf
2010-07-01T10:43:09Z

The PowerPC ISA has a special instruction for mtmsr that only changes the EE
and RI bits, namely the L=1 form.

Since that one is reasonably often occuring and simple to implement, let's
go with this first. Writing EE=0 is always just a store. Doing EE=1 also
requires us to check for pending interrupts and if necessary exit back to the
hypervisor.

Signed-off-by: Alexander Graf <agraf@suse.de>

---

v1 -> v2:

- use kvm_patch_ins_b
---
arch/powerpc/kernel/kvm.c | 45 ++++++++++++++++++++++++++++++++
arch/powerpc/kernel/kvm_emul.S | 56 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 101 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/kernel/kvm.c b/arch/powerpc/kernel/kvm.c
index 337e3e5..1e32298 100644
--- a/arch/powerpc/kernel/kvm.c
+++ b/arch/powerpc/kernel/kvm.c
@@ -62,6 +62,7 @@
#define KVM_INST_MTSPR_DSISR 0x7c1203a6

#define KVM_INST_TLBSYNC 0x7c00046c
+#define KVM_INST_MTMSRD_L1 0x7c010164

static bool kvm_patching_worked = true;
static char kvm_tmp[1024 * 1024];
@@ -128,6 +129,43 @@ static u32 *kvm_alloc(int len)
return p;
}

+extern u32 kvm_emulate_mtmsrd_branch_offs;
+extern u32 kvm_emulate_mtmsrd_reg_offs;
+extern u32 kvm_emulate_mtmsrd_len;
+extern u32 kvm_emulate_mtmsrd[];
+
+static void kvm_patch_ins_mtmsrd(u32 *inst, u32 rt)
+{
+ u32 *p;
+ int distance_start;
+ int distance_end;
+ ulong next_inst;
+
+ p = kvm_alloc(kvm_emulate_mtmsrd_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_mtmsrd_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_mtmsrd, kvm_emulate_mtmsrd_len * 4);
+ p[kvm_emulate_mtmsrd_branch_offs] |= distance_end & KVM_INST_B_MASK;
+ p[kvm_emulate_mtmsrd_reg_offs] |= rt;
+ flush_icache_range((ulong)p, (ulong)p + kvm_emulate_mtmsrd_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,
@@ -201,6 +239,13 @@ static void kvm_check_ins(u32 *inst)
case KVM_INST_TLBSYNC:
kvm_patch_ins_nop(inst);
break;
+
+ /* Rewrites */
+ case KVM_INST_MTMSRD_L1:
+ /* We use r30 and r31 during the hook */
+ if (get_rt(inst_rt) < 30)
+ kvm_patch_ins_mtmsrd(inst, inst_rt);
+ break;
}

switch (_inst) {
diff --git a/arch/powerpc/kernel/kvm_emul.S b/arch/powerpc/kernel/kvm_emul.S
index 7da835a..25e6683 100644
--- a/arch/powerpc/kernel/kvm_emul.S
+++ b/arch/powerpc/kernel/kvm_emul.S
@@ -54,3 +54,59 @@
/* Disable critical section. We are critical if \
shared->critical == r1 and r2 is always != r1 */ \
STL64(r2, KVM_MAGIC_PAGE + KVM_MAGIC_CRITICAL, 0);
+
+.global kvm_emulate_mtmsrd
+kvm_emulate_mtmsrd:
+
+ SCRATCH_SAVE
+
+ /* Put MSR & ~(MSR_EE|MSR_RI) in r31 */
+ LL64(r31, KVM_MAGIC_PAGE + KVM_MAGIC_MSR, 0)
+ lis r30, (~(MSR_EE | MSR_RI))@h
+ ori r30, r30, (~(MSR_EE | MSR_RI))@l
+ and r31, r31, r30
+
+ /* OR the register's (MSR_EE|MSR_RI) on MSR */
+kvm_emulate_mtmsrd_reg:
+ andi. r30, r0, (MSR_EE|MSR_RI)
+ or r31, r31, r30
+
+ /* Put MSR back into magic page */
+ STL64(r31, KVM_MAGIC_PAGE + KVM_MAGIC_MSR, 0)
+
+ /* Check if we have to fetch an interrupt */
+ lwz r31, (KVM_MAGIC_PAGE + KVM_MAGIC_INT)(0)
+ cmpwi r31, 0
+ beq+ no_check
+
+ /* Check if we may trigger an interrupt */
+ andi. r30, r30, MSR_EE
+ beq no_check
+
+ SCRATCH_RESTORE
+
+ /* Nag hypervisor */
+ tlbsync
+
+ b kvm_emulate_mtmsrd_branch
+
+no_check:
+
+ SCRATCH_RESTORE
+
+ /* Go back to caller */
+kvm_emulate_mtmsrd_branch:
+ b .
+kvm_emulate_mtmsrd_end:
+
+.global kvm_emulate_mtmsrd_branch_offs
+kvm_emulate_mtmsrd_branch_offs:
+ .long (kvm_emulate_mtmsrd_branch - kvm_emulate_mtmsrd) / 4
+
+.global kvm_emulate_mtmsrd_reg_offs
+kvm_emulate_mtmsrd_reg_offs:
+ .long (kvm_emulate_mtmsrd_reg - kvm_emulate_mtmsrd) / 4
+
+.global kvm_emulate_mtmsrd_len
+kvm_emulate_mtmsrd_len:
+ .long (kvm_emulate_mtmsrd_end - kvm_emulate_mtmsrd) / 4
--
1.6.0.2