KVM: PPC: Book3S HV: Make HPT reading code notice R/C bit changes

At present, the code that determines whether a HPT entry has changed,
and thus needs to be sent to userspace when it is copying the HPT,
doesn't consider a hardware update to the reference and change bits
(R and C) in the HPT entries to constitute a change that needs to
be sent to userspace.  This adds code to check for changes in R and C
when we are scanning the HPT to find changed entries, and adds code
to set the changed flag for the HPTE when we update the R and C bits
in the guest view of the HPTE.

Since we now need to set the HPTE changed flag in book3s_64_mmu_hv.c
as well as book3s_hv_rm_mmu.c, we move the note_hpte_modification()
function into kvm_book3s_64.h.

Current Linux guest kernels don't use the hardware updates of R and C
in the HPT, so this change won't affect them.  Linux (or other) kernels
might in future want to use the R and C bits and have them correctly
transferred across when a guest is migrated, so it is better to correct
this deficiency.

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

3 files changed, 63 insertions, 20 deletions

diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
index 38bec1dc9928..9c1ff330c805 100644
--- a/arch/powerpc/include/asm/kvm_book3s_64.h
+++ b/arch/powerpc/include/asm/kvm_book3s_64.h
@@ -268,4 +268,17 @@ static inline int is_vrma_hpte(unsigned long hpte_v)
                 (HPTE_V_1TB_SEG | (VRMA_VSID << (40 - 16)));
 }
 
+#ifdef CONFIG_KVM_BOOK3S_64_HV
+/*
+ * 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;
+}
+#endif /* CONFIG_KVM_BOOK3S_64_HV */
+
 #endif /* __ASM_KVM_BOOK3S_64_H__ */
diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 8cc18abd6dde..d641a6634b02 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -893,7 +893,10 @@ static int kvm_unmap_rmapp(struct kvm *kvm, unsigned long *rmapp,
                         /* Harvest R and C */
                         rcbits = hptep[1] & (HPTE_R_R | HPTE_R_C);
                         *rmapp |= rcbits << KVMPPC_RMAP_RC_SHIFT;
-                        rev[i].guest_rpte = ptel | rcbits;
+                        if (rcbits & ~rev[i].guest_rpte) {
+                                rev[i].guest_rpte = ptel | rcbits;
+                                note_hpte_modification(kvm, &rev[i]);
+                        }
                 }
                 unlock_rmap(rmapp);
                 hptep[0] &= ~HPTE_V_HVLOCK;
@@ -976,7 +979,10 @@ static int kvm_age_rmapp(struct kvm *kvm, unsigned long *rmapp,
                 /* Now check and modify the HPTE */
                 if ((hptep[0] & HPTE_V_VALID) && (hptep[1] & HPTE_R_R)) {
                         kvmppc_clear_ref_hpte(kvm, hptep, i);
-                        rev[i].guest_rpte |= HPTE_R_R;
+                        if (!(rev[i].guest_rpte & HPTE_R_R)) {
+                                rev[i].guest_rpte |= HPTE_R_R;
+                                note_hpte_modification(kvm, &rev[i]);
+                        }
                         ret = 1;
                 }
                 hptep[0] &= ~HPTE_V_HVLOCK;
@@ -1080,7 +1086,10 @@ static int kvm_test_clear_dirty(struct kvm *kvm, unsigned long *rmapp)
                         hptep[1] &= ~HPTE_R_C;
                         eieio();
                         hptep[0] = (hptep[0] & ~HPTE_V_ABSENT) | HPTE_V_VALID;
-                        rev[i].guest_rpte |= HPTE_R_C;
+                        if (!(rev[i].guest_rpte & HPTE_R_C)) {
+                                rev[i].guest_rpte |= HPTE_R_C;
+                                note_hpte_modification(kvm, &rev[i]);
+                        }
                         ret = 1;
                 }
                 hptep[0] &= ~HPTE_V_HVLOCK;
@@ -1193,16 +1202,36 @@ struct kvm_htab_ctx {
 
 #define HPTE_SIZE       (2 * sizeof(unsigned long))
 
+/*
+ * Returns 1 if this HPT entry has been modified or has pending
+ * R/C bit changes.
+ */
+static int hpte_dirty(struct revmap_entry *revp, unsigned long *hptp)
+{
+        unsigned long rcbits_unset;
+
+        if (revp->guest_rpte & HPTE_GR_MODIFIED)
+                return 1;
+
+        /* Also need to consider changes in reference and changed bits */
+        rcbits_unset = ~revp->guest_rpte & (HPTE_R_R | HPTE_R_C);
+        if ((hptp[0] & HPTE_V_VALID) && (hptp[1] & rcbits_unset))
+                return 1;
+
+        return 0;
+}
+
 static long record_hpte(unsigned long flags, unsigned long *hptp,
                         unsigned long *hpte, struct revmap_entry *revp,
                         int want_valid, int first_pass)
 {
         unsigned long v, r;
+        unsigned long rcbits_unset;
         int ok = 1;
         int valid, dirty;
 
         /* Unmodified entries are uninteresting except on the first pass */
-        dirty = !!(revp->guest_rpte & HPTE_GR_MODIFIED);
+        dirty = hpte_dirty(revp, hptp);
         if (!first_pass && !dirty)
                 return 0;
 
@@ -1223,16 +1252,28 @@ static long record_hpte(unsigned long flags, unsigned long *hptp,
                 while (!try_lock_hpte(hptp, HPTE_V_HVLOCK))
                         cpu_relax();
                 v = hptp[0];
+
+                /* re-evaluate valid and dirty from synchronized HPTE value */
+                valid = !!(v & HPTE_V_VALID);
+                dirty = !!(revp->guest_rpte & HPTE_GR_MODIFIED);
+
+                /* Harvest R and C into guest view if necessary */
+                rcbits_unset = ~revp->guest_rpte & (HPTE_R_R | HPTE_R_C);
+                if (valid && (rcbits_unset & hptp[1])) {
+                        revp->guest_rpte |= (hptp[1] & (HPTE_R_R | HPTE_R_C)) |
+                                HPTE_GR_MODIFIED;
+                        dirty = 1;
+                }
+
                 if (v & HPTE_V_ABSENT) {
                         v &= ~HPTE_V_ABSENT;
                         v |= HPTE_V_VALID;
+                        valid = 1;
                 }
-                /* re-evaluate valid and dirty from synchronized HPTE value */
-                valid = !!(v & HPTE_V_VALID);
                 if ((flags & KVM_GET_HTAB_BOLTED_ONLY) && !(v & HPTE_V_BOLTED))
                         valid = 0;
-                r = revp->guest_rpte | (hptp[1] & (HPTE_R_R | HPTE_R_C));
-                dirty = !!(revp->guest_rpte & HPTE_GR_MODIFIED);
+
+                r = revp->guest_rpte;
                 /* only clear modified if this is the right sort of entry */
                 if (valid == want_valid && dirty) {
                         r &= ~HPTE_GR_MODIFIED;
@@ -1288,7 +1329,7 @@ static ssize_t kvm_htab_read(struct file *file, char __user *buf,
                 /* Skip uninteresting entries, i.e. clean on not-first pass */
                 if (!first_pass) {
                         while (i < kvm->arch.hpt_npte &&
-                               !(revp->guest_rpte & HPTE_GR_MODIFIED)) {
+                               !hpte_dirty(revp, hptp)) {
                                 ++i;
                                 hptp += 2;
                                 ++revp;
diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
index 19c93bae1aea..6dcbb49105a4 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
@@ -97,17 +97,6 @@ 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,