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[PATCH v3 05/11] KVM: page track: introduce kvm_page_track_{add,remove}_page

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  [PATCH v3 05/11] KVM: page track: introduce kvm_page_track_{add,remove}_page Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2016-02-14 12:50 +0100
    Re: [PATCH v3 05/11] KVM: page track: introduce  kvm_page_track_{add,remove}_page Paolo Bonzini <pbonzini@redhat.com> - 2016-02-19 12:40 +0100
    Re: [PATCH v3 05/11] KVM: page track: introduce  kvm_page_track_{add,remove}_page Paolo Bonzini <pbonzini@redhat.com> - 2016-02-19 12:40 +0100

#1333486 — [PATCH v3 05/11] KVM: page track: introduce kvm_page_track_{add,remove}_page

These two functions are the user APIs:
- kvm_page_track_add_page(): add the page to the tracking pool after
  that later specified access on that page will be tracked

- kvm_page_track_remove_page(): remove the page from the tracking pool,
  the specified access on the page is not tracked after the last user is
  gone

Both of these are called under the protection of kvm->srcu or
kvm->slots_lock

Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
---
 arch/x86/include/asm/kvm_page_track.h |  13 ++++
 arch/x86/kvm/page_track.c             | 124 ++++++++++++++++++++++++++++++++++
 2 files changed, 137 insertions(+)

diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index 55200406..c010124 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -10,4 +10,17 @@ void kvm_page_track_free_memslot(struct kvm_memory_slot *free,
 				 struct kvm_memory_slot *dont);
 int kvm_page_track_create_memslot(struct kvm_memory_slot *slot,
 				  unsigned long npages);
+
+void
+kvm_slot_page_track_add_page_nolock(struct kvm *kvm,
+				    struct kvm_memory_slot *slot, gfn_t gfn,
+				    enum kvm_page_track_mode mode);
+void kvm_page_track_add_page(struct kvm *kvm, gfn_t gfn,
+			     enum kvm_page_track_mode mode);
+void kvm_slot_page_track_remove_page_nolock(struct kvm *kvm,
+					    struct kvm_memory_slot *slot,
+					    gfn_t gfn,
+					    enum kvm_page_track_mode mode);
+void kvm_page_track_remove_page(struct kvm *kvm, gfn_t gfn,
+				enum kvm_page_track_mode mode);
 #endif
diff --git a/arch/x86/kvm/page_track.c b/arch/x86/kvm/page_track.c
index 8c396d0..e17efe9 100644
--- a/arch/x86/kvm/page_track.c
+++ b/arch/x86/kvm/page_track.c
@@ -50,3 +50,127 @@ track_free:
 	kvm_page_track_free_memslot(slot, NULL);
 	return -ENOMEM;
 }
+
+static bool check_mode(enum kvm_page_track_mode mode)
+{
+	if (mode < 0 || mode >= KVM_PAGE_TRACK_MAX)
+		return false;
+
+	return true;
+}
+
+static void update_gfn_track(struct kvm_memory_slot *slot, gfn_t gfn,
+			     enum kvm_page_track_mode mode, short count)
+{
+	int index;
+	unsigned short val;
+
+	index = gfn_to_index(gfn, slot->base_gfn, PT_PAGE_TABLE_LEVEL);
+
+	val = slot->arch.gfn_track[mode][index];
+
+	/* does tracking count wrap? */
+	WARN_ON((count > 0) && (val + count < val));
+	/* the last tracker has already gone? */
+	WARN_ON((count < 0) && (val < !count));
+
+	slot->arch.gfn_track[mode][index] += count;
+}
+
+void
+kvm_slot_page_track_add_page_nolock(struct kvm *kvm,
+				    struct kvm_memory_slot *slot, gfn_t gfn,
+				    enum kvm_page_track_mode mode)
+{
+
+	WARN_ON(!check_mode(mode));
+
+	update_gfn_track(slot, gfn, mode, 1);
+
+	/*
+	 * new track stops large page mapping for the
+	 * tracked page.
+	 */
+	kvm_mmu_gfn_disallow_lpage(slot, gfn);
+
+	if (mode == KVM_PAGE_TRACK_WRITE)
+		if (kvm_mmu_slot_gfn_write_protect(kvm, slot, gfn))
+			kvm_flush_remote_tlbs(kvm);
+}
+
+/*
+ * add guest page to the tracking pool so that corresponding access on that
+ * page will be intercepted.
+ *
+ * It should be called under the protection of kvm->srcu or kvm->slots_lock
+ *
+ * @kvm: the guest instance we are interested in.
+ * @gfn: the guest page.
+ * @mode: tracking mode, currently only write track is supported.
+ */
+void kvm_page_track_add_page(struct kvm *kvm, gfn_t gfn,
+			     enum kvm_page_track_mode mode)
+{
+	struct kvm_memslots *slots;
+	struct kvm_memory_slot *slot;
+	int i;
+
+	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
+		slots = __kvm_memslots(kvm, i);
+
+		slot = __gfn_to_memslot(slots, gfn);
+		if (!slot)
+			continue;
+
+		spin_lock(&kvm->mmu_lock);
+		kvm_slot_page_track_add_page_nolock(kvm, slot, gfn, mode);
+		spin_unlock(&kvm->mmu_lock);
+	}
+}
+
+void kvm_slot_page_track_remove_page_nolock(struct kvm *kvm,
+					    struct kvm_memory_slot *slot,
+					    gfn_t gfn,
+					    enum kvm_page_track_mode mode)
+{
+	WARN_ON(!check_mode(mode));
+
+	update_gfn_track(slot, gfn, mode, -1);
+
+	/*
+	 * allow large page mapping for the tracked page
+	 * after the tracker is gone.
+	 */
+	kvm_mmu_gfn_allow_lpage(slot, gfn);
+}
+
+/*
+ * remove the guest page from the tracking pool which stops the interception
+ * of corresponding access on that page. It is the opposed operation of
+ * kvm_page_track_add_page().
+ *
+ * It should be called under the protection of kvm->srcu or kvm->slots_lock
+ *
+ * @kvm: the guest instance we are interested in.
+ * @gfn: the guest page.
+ * @mode: tracking mode, currently only write track is supported.
+ */
+void kvm_page_track_remove_page(struct kvm *kvm, gfn_t gfn,
+				enum kvm_page_track_mode mode)
+{
+	struct kvm_memslots *slots;
+	struct kvm_memory_slot *slot;
+	int i;
+
+	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
+		slots = __kvm_memslots(kvm, i);
+
+		slot = __gfn_to_memslot(slots, gfn);
+		if (!slot)
+			continue;
+
+		spin_lock(&kvm->mmu_lock);
+		kvm_slot_page_track_remove_page_nolock(kvm, slot, gfn, mode);
+		spin_unlock(&kvm->mmu_lock);
+	}
+}
-- 
1.8.3.1

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#1338066 — Re: [PATCH v3 05/11] KVM: page track: introduce kvm_page_track_{add,remove}_page

On 14/02/2016 12:31, Xiao Guangrong wrote:
> +static bool check_mode(enum kvm_page_track_mode mode)
> +{
> +	if (mode < 0 || mode >= KVM_PAGE_TRACK_MAX)
> +		return false;
> +
> +	return true;
> +}

Oops, forgot about this; please rename to page_track_mode_is_valid and
make it "static inline".

Paolo

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#1338067 — Re: [PATCH v3 05/11] KVM: page track: introduce kvm_page_track_{add,remove}_page

On 14/02/2016 12:31, Xiao Guangrong wrote:
> +	/* does tracking count wrap? */
> +	WARN_ON((count > 0) && (val + count < val));

This doesn't work, because "val + count" is an int.

> +	/* the last tracker has already gone? */
> +	WARN_ON((count < 0) && (val < !count));

Also, here any underflow should warn.

You can actually use the fact that val + count is an int like this:

    WARN_ON(val + count < 0 || val + count > USHRT_MAX)

and also please return if the warning fires.

> +void kvm_page_track_add_page(struct kvm *kvm, gfn_t gfn,
> +			     enum kvm_page_track_mode mode)
> +{
> +	struct kvm_memslots *slots;
> +	struct kvm_memory_slot *slot;
> +	int i;
> +
> +	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> +		slots = __kvm_memslots(kvm, i);
> +
> +		slot = __gfn_to_memslot(slots, gfn);
> +		if (!slot)
> +			continue;
> +
> +		spin_lock(&kvm->mmu_lock);
> +		kvm_slot_page_track_add_page_nolock(kvm, slot, gfn, mode);
> +		spin_unlock(&kvm->mmu_lock);
> +	}
> +}

I don't think it is right to walk all address spaces.  The good news is
that you're not using kvm_page_track_{add,remove}_page at all as far as
I can see, so you can just remove them.

Also, when you will need it, I think it's better to move the
spin_lock/spin_unlock pair outside the for loop.  With this change,
perhaps it's better to leave it to the caller completely---but I cannot
say until I see the caller.

In the meanwhile, please leave out _nolock from the other functions' name.

Paolo

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