KVM: PPC: Book3S PR: Use SLB entry 0

Commit Message

Alexander Graf May 15, 2014, 12:43 p.m. UTC

We didn't make use of SLB entry 0 because ... of no good reason. SLB entry 0
will always be used by the Linux linear SLB entry, so the fact that slbia
does not invalidate it doesn't matter as we overwrite SLB 0 on exit anyway.

Just enable use of SLB entry 0 for our shadow SLB code.

Signed-off-by: Alexander Graf <[e-mail]>
---
 arch/powerpc/kvm/book3s_64_mmu_host.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

Comments

Paul Mackerras May 17, 2014, 5:26 a.m. UTC | #1

On Thu, May 15, 2014 at 02:43:51PM +0200, Alexander Graf wrote:
> We didn't make use of SLB entry 0 because ... of no good reason. SLB entry 0
> will always be used by the Linux linear SLB entry, so the fact that slbia
> does not invalidate it doesn't matter as we overwrite SLB 0 on exit anyway.
> 
> Just enable use of SLB entry 0 for our shadow SLB code.

I think that this is a good idea, but to be sure of invalidating all
ERAT entries you should write zeroes to SLB entry 0 before the slbia
on guest exit.

Paul.
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Patch

diff --git a/arch/powerpc/kvm/book3s_64_mmu_host.c b/arch/powerpc/kvm/book3s_64_mmu_host.c
index e2efb85..0ac9839 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_host.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_host.c
@@ -271,11 +271,8 @@  static int kvmppc_mmu_next_segment(struct kvm_vcpu *vcpu, ulong esid)
 	int found_inval = -1;
 	int r;
 
-	if (!svcpu->slb_max)
-		svcpu->slb_max = 1;
-
 	/* Are we overwriting? */
-	for (i = 1; i < svcpu->slb_max; i++) {
+	for (i = 0; i < svcpu->slb_max; i++) {
 		if (!(svcpu->slb[i].esid & SLB_ESID_V))
 			found_inval = i;
 		else if ((svcpu->slb[i].esid & ESID_MASK) == esid) {
@@ -285,7 +282,7 @@  static int kvmppc_mmu_next_segment(struct kvm_vcpu *vcpu, ulong esid)
 	}
 
 	/* Found a spare entry that was invalidated before */
-	if (found_inval > 0) {
+	if (found_inval >= 0) {
 		r = found_inval;
 		goto out;
 	}
@@ -359,7 +356,7 @@  void kvmppc_mmu_flush_segment(struct kvm_vcpu *vcpu, ulong ea, ulong seg_size)
 	ulong seg_mask = -seg_size;
 	int i;
 
-	for (i = 1; i < svcpu->slb_max; i++) {
+	for (i = 0; i < svcpu->slb_max; i++) {
 		if ((svcpu->slb[i].esid & SLB_ESID_V) &&
 		    (svcpu->slb[i].esid & seg_mask) == ea) {
 			/* Invalidate this entry */
@@ -373,7 +370,7 @@  void kvmppc_mmu_flush_segment(struct kvm_vcpu *vcpu, ulong ea, ulong seg_size)
 void kvmppc_mmu_flush_segments(struct kvm_vcpu *vcpu)
 {
 	struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
-	svcpu->slb_max = 1;
+	svcpu->slb_max = 0;
 	svcpu->slb[0].esid = 0;
 	svcpu_put(svcpu);
 }