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>

2 files changed, 10 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
index 1472a5b4e4e..b322e5bd696 100644
--- a/arch/powerpc/include/asm/kvm_book3s_64.h
+++ b/arch/powerpc/include/asm/kvm_book3s_64.h
@@ -50,6 +50,15 @@ extern int kvm_hpt_order;		/* order of preallocated HPTs */
 #define HPTE_V_HVLOCK	0x40UL
 #define HPTE_V_ABSENT	0x20UL
 
+/*
+ * We use this bit in the guest_rpte field of the revmap entry
+ * to indicate a modified HPTE.
+ */
+#define HPTE_GR_MODIFIED	(1ul << 62)
+
+/* These bits are reserved in the guest view of the HPTE */
+#define HPTE_GR_RESERVED	HPTE_GR_MODIFIED
+
 static inline long try_lock_hpte(unsigned long *hpte, unsigned long bits)
 {
 	unsigned long tmp, old;
diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 3093896015f..58c72646c44 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -248,6 +248,7 @@ struct kvm_arch {
 	atomic_t vcpus_running;
 	unsigned long hpt_npte;
 	unsigned long hpt_mask;
+	atomic_t hpte_mod_interest;
 	spinlock_t slot_phys_lock;
 	unsigned short last_vcpu[NR_CPUS];
 	struct kvmppc_vcore *vcores[KVM_MAX_VCORES];