KVM: PPC: Book3S HV: Add a mechanism for recording modified HPTEs

This uses a bit in our record of the guest view of the HPTE to record
when the HPTE gets modified.  We use a reserved bit for this, and ensure
that this bit is always cleared in HPTE values returned to the guest.

The recording of modified HPTEs is only done if other code indicates
its interest by setting kvm->arch.hpte_mod_interest to a non-zero value.
The reason for this is that when later commits add facilities for
userspace to read the HPT, the first pass of reading the HPT will be
quicker if there are no (or very few) HPTEs marked as modified,
rather than having most HPTEs marked as modified.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 24 insertions, 4 deletions

diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
index ff2da5c..ed563a5 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
@@ -66,6 +66,17 @@ void kvmppc_add_revmap_chain(struct kvm *kvm, struct revmap_entry *rev,
 }
 EXPORT_SYMBOL_GPL(kvmppc_add_revmap_chain);
 
+/*
+ * Note modification of an HPTE; set the HPTE modified bit
+ * if anyone is interested.
+ */
+static inline void note_hpte_modification(struct kvm *kvm,
+					  struct revmap_entry *rev)
+{
+	if (atomic_read(&kvm->arch.hpte_mod_interest))
+		rev->guest_rpte |= HPTE_GR_MODIFIED;
+}
+
 /* Remove this HPTE from the chain for a real page */
 static void remove_revmap_chain(struct kvm *kvm, long pte_index,
 				struct revmap_entry *rev,
@@ -138,7 +149,7 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
 	unsigned long slot_fn, hva;
 	unsigned long *hpte;
 	struct revmap_entry *rev;
-	unsigned long g_ptel = ptel;
+	unsigned long g_ptel;
 	struct kvm_memory_slot *memslot;
 	unsigned long *physp, pte_size;
 	unsigned long is_io;
@@ -153,6 +164,8 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
 		return H_PARAMETER;
 	writing = hpte_is_writable(ptel);
 	pteh &= ~(HPTE_V_HVLOCK | HPTE_V_ABSENT | HPTE_V_VALID);
+	ptel &= ~HPTE_GR_RESERVED;
+	g_ptel = ptel;
 
 	/* used later to detect if we might have been invalidated */
 	mmu_seq = kvm->mmu_notifier_seq;
@@ -287,8 +300,10 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
 	rev = &kvm->arch.revmap[pte_index];
 	if (realmode)
 		rev = real_vmalloc_addr(rev);
-	if (rev)
+	if (rev) {
 		rev->guest_rpte = g_ptel;
+		note_hpte_modification(kvm, rev);
+	}
 
 	/* Link HPTE into reverse-map chain */
 	if (pteh & HPTE_V_VALID) {
@@ -392,7 +407,8 @@ long kvmppc_h_remove(struct kvm_vcpu *vcpu, unsigned long flags,
 		/* Read PTE low word after tlbie to get final R/C values */
 		remove_revmap_chain(kvm, pte_index, rev, v, hpte[1]);
 	}
-	r = rev->guest_rpte;
+	r = rev->guest_rpte & ~HPTE_GR_RESERVED;
+	note_hpte_modification(kvm, rev);
 	unlock_hpte(hpte, 0);
 
 	vcpu->arch.gpr[4] = v;
@@ -466,6 +482,7 @@ long kvmppc_h_bulk_remove(struct kvm_vcpu *vcpu)
 
 			args[j] = ((0x80 | flags) << 56) + pte_index;
 			rev = real_vmalloc_addr(&kvm->arch.revmap[pte_index]);
+			note_hpte_modification(kvm, rev);
 
 			if (!(hp[0] & HPTE_V_VALID)) {
 				/* insert R and C bits from PTE */
@@ -555,6 +572,7 @@ long kvmppc_h_protect(struct kvm_vcpu *vcpu, unsigned long flags,
 	if (rev) {
 		r = (rev->guest_rpte & ~mask) | bits;
 		rev->guest_rpte = r;
+		note_hpte_modification(kvm, rev);
 	}
 	r = (hpte[1] & ~mask) | bits;
 
@@ -606,8 +624,10 @@ long kvmppc_h_read(struct kvm_vcpu *vcpu, unsigned long flags,
 			v &= ~HPTE_V_ABSENT;
 			v |= HPTE_V_VALID;
 		}
-		if (v & HPTE_V_VALID)
+		if (v & HPTE_V_VALID) {
 			r = rev[i].guest_rpte | (r & (HPTE_R_R | HPTE_R_C));
+			r &= ~HPTE_GR_RESERVED;
+		}
 		vcpu->arch.gpr[4 + i * 2] = v;
 		vcpu->arch.gpr[5 + i * 2] = r;
 	}