Subject: [PATCH v1 2/4] KVM: PPC: Book3S HV: track shared GFNs of secure VMs

From: Ram Pai <[email-masked]>
Date: Sat, 30 May 2020 19:27:49 -0700

During the life of SVM, its GFNs can transition from secure to shared
state and vice-versa. Since the kernel does not track GFNs that are
shared, it is not possible to disambiguate a shared GFN from a GFN whose
PFN has not yet been migrated to a device-PFN.

The ability to identify a shared GFN is needed to skip migrating its PFN
to device PFN. This functionality is leveraged in a subsequent patch.

Add the ability to identify the state of a GFN.

Cc: Paul Mackerras <[email-masked]>
Cc: Benjamin Herrenschmidt <[email-masked]>
Cc: Michael Ellerman <[email-masked]>
Cc: Bharata B Rao <[email-masked]>
Cc: Aneesh Kumar K.V <[email-masked]>
Cc: Sukadev Bhattiprolu <[email-masked]>
Cc: Laurent Dufour <[email-masked]>
Cc: Thiago Jung Bauermann <[email-masked]>
Cc: David Gibson <[email-masked]>
Cc: Claudio Carvalho <[email-masked]>
Cc: [email-masked]
Cc: [email-masked]
Reviewed-by: Thiago Jung Bauermann <[email-masked]>
Signed-off-by: Ram Pai <[email-masked]>
---
 arch/powerpc/include/asm/kvm_book3s_uvmem.h |   6 +-
 arch/powerpc/kvm/book3s_64_mmu_radix.c      |   2 +-
 arch/powerpc/kvm/book3s_hv.c                |   2 +-
 arch/powerpc/kvm/book3s_hv_uvmem.c          | 115 ++++++++++++++++++++++++++--
 4 files changed, 113 insertions(+), 12 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_book3s_uvmem.h b/arch/powerpc/include/asm/kvm_book3s_uvmem.h
index 5a9834e..f0c5708 100644
--- a/arch/powerpc/include/asm/kvm_book3s_uvmem.h
+++ b/arch/powerpc/include/asm/kvm_book3s_uvmem.h
@@ -21,7 +21,8 @@ unsigned long kvmppc_h_svm_page_out(struct kvm *kvm,
 int kvmppc_send_page_to_uv(struct kvm *kvm, unsigned long gfn);
 unsigned long kvmppc_h_svm_init_abort(struct kvm *kvm);
 void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *free,
-			     struct kvm *kvm, bool skip_page_out);
+			     struct kvm *kvm, bool skip_page_out,
+			     bool purge_gfn);
 #else
 static inline int kvmppc_uvmem_init(void)
 {
@@ -75,6 +76,7 @@ static inline int kvmppc_send_page_to_uv(struct kvm *kvm, unsigned long gfn)
 
 static inline void
 kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *free,
-			struct kvm *kvm, bool skip_page_out) { }
+			struct kvm *kvm, bool skip_page_out,
+			bool purge_gfn) { }
 #endif /* CONFIG_PPC_UV */
 #endif /* __ASM_KVM_BOOK3S_UVMEM_H__ */
diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index 803940d..3448459 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -1100,7 +1100,7 @@ void kvmppc_radix_flush_memslot(struct kvm *kvm,
 	unsigned int shift;
 
 	if (kvm->arch.secure_guest & KVMPPC_SECURE_INIT_START)
-		kvmppc_uvmem_drop_pages(memslot, kvm, true);
+		kvmppc_uvmem_drop_pages(memslot, kvm, true, false);
 
 	if (kvm->arch.secure_guest & KVMPPC_SECURE_INIT_DONE)
 		return;
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 103d13e..4c62bfe 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -5467,7 +5467,7 @@ static int kvmhv_svm_off(struct kvm *kvm)
 			continue;
 
 		kvm_for_each_memslot(memslot, slots) {
-			kvmppc_uvmem_drop_pages(memslot, kvm, true);
+			kvmppc_uvmem_drop_pages(memslot, kvm, true, true);
 			uv_unregister_mem_slot(kvm->arch.lpid, memslot->id);
 		}
 	}
diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index ea4a1f1..2ef1e03 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -99,14 +99,56 @@
 static DEFINE_SPINLOCK(kvmppc_uvmem_bitmap_lock);
 
 #define KVMPPC_UVMEM_PFN	(1UL << 63)
+#define KVMPPC_UVMEM_SHARED	(1UL << 62)
+#define KVMPPC_UVMEM_FLAG_MASK	(KVMPPC_UVMEM_PFN | KVMPPC_UVMEM_SHARED)
+#define KVMPPC_UVMEM_PFN_MASK	(~KVMPPC_UVMEM_FLAG_MASK)
 
 struct kvmppc_uvmem_slot {
 	struct list_head list;
 	unsigned long nr_pfns;
 	unsigned long base_pfn;
+	/*
+	 * pfns array has an entry for each GFN of the memory slot.
+	 *
+	 * The GFN can be in one of the following states.
+	 *
+	 * (a) Secure - The GFN is secure. Only Ultravisor can access it.
+	 * (b) Shared - The GFN is shared. Both Hypervisor and Ultravisor
+	 *		can access it.
+	 * (c) Normal - The GFN is a normal.  Only Hypervisor can access it.
+	 *
+	 * Secure GFN is associated with a devicePFN. Its pfn[] has
+	 * KVMPPC_UVMEM_PFN flag set, and has the value of the device PFN
+	 * KVMPPC_UVMEM_SHARED flag unset, and has the value of the device PFN
+	 *
+	 * Shared GFN is associated with a memoryPFN. Its pfn[] has
+	 * KVMPPC_UVMEM_SHARED flag set. But its KVMPPC_UVMEM_PFN is not set,
+	 * and there is no PFN value stored.
+	 *
+	 * Normal GFN is not associated with memoryPFN. Its pfn[] has
+	 * KVMPPC_UVMEM_SHARED and KVMPPC_UVMEM_PFN flag unset, and no PFN
+	 * value is stored.
+	 *
+	 * Any other combination of values in pfn[] leads to undefined
+	 * behavior.
+	 *
+	 * Life cycle of a GFN --
+	 *
+	 * ---------------------------------------------------------
+	 * |        |     Share	 |  Unshare | SVM	|slot      |
+	 * |	    |		 |	    | abort/	|flush	   |
+	 * |	    |		 |	    | terminate	|	   |
+	 * ---------------------------------------------------------
+	 * |        |            |          |           |          |
+	 * | Secure |     Shared | Secure   |Normal	|Secure    |
+	 * |        |            |          |           |          |
+	 * | Shared |     Shared | Secure   |Normal     |Shared    |
+	 * |        |            |          |           |          |
+	 * | Normal |     Shared | Secure   |Normal     |Normal    |
+	 * ---------------------------------------------------------
+	 */
 	unsigned long *pfns;
 };
-
 struct kvmppc_uvmem_page_pvt {
 	struct kvm *kvm;
 	unsigned long gpa;
@@ -175,7 +217,12 @@ static void kvmppc_uvmem_pfn_remove(unsigned long gfn, struct kvm *kvm)
 
 	list_for_each_entry(p, &kvm->arch.uvmem_pfns, list) {
 		if (gfn >= p->base_pfn && gfn < p->base_pfn + p->nr_pfns) {
-			p->pfns[gfn - p->base_pfn] = 0;
+			/*
+			 * Reset everything, but keep the KVMPPC_UVMEM_SHARED
+			 * flag intact.  A gfn continues to be shared or
+			 * unshared, with or without an associated device pfn.
+			 */
+			p->pfns[gfn - p->base_pfn] &= KVMPPC_UVMEM_SHARED;
 			return;
 		}
 	}
@@ -193,7 +240,7 @@ static bool kvmppc_gfn_is_uvmem_pfn(unsigned long gfn, struct kvm *kvm,
 			if (p->pfns[index] & KVMPPC_UVMEM_PFN) {
 				if (uvmem_pfn)
 					*uvmem_pfn = p->pfns[index] &
-						     ~KVMPPC_UVMEM_PFN;
+						     KVMPPC_UVMEM_PFN_MASK;
 				return true;
 			} else
 				return false;
@@ -202,6 +249,38 @@ static bool kvmppc_gfn_is_uvmem_pfn(unsigned long gfn, struct kvm *kvm,
 	return false;
 }
 
+static void kvmppc_gfn_uvmem_shared(unsigned long gfn, struct kvm *kvm,
+		bool set)
+{
+	struct kvmppc_uvmem_slot *p;
+
+	list_for_each_entry(p, &kvm->arch.uvmem_pfns, list) {
+		if (gfn >= p->base_pfn && gfn < p->base_pfn + p->nr_pfns) {
+			unsigned long index = gfn - p->base_pfn;
+
+			if (set)
+				p->pfns[index] |= KVMPPC_UVMEM_SHARED;
+			else
+				p->pfns[index] &= ~KVMPPC_UVMEM_SHARED;
+			return;
+		}
+	}
+}
+
+bool kvmppc_gfn_is_uvmem_shared(unsigned long gfn, struct kvm *kvm)
+{
+	struct kvmppc_uvmem_slot *p;
+
+	list_for_each_entry(p, &kvm->arch.uvmem_pfns, list) {
+		if (gfn >= p->base_pfn && gfn < p->base_pfn + p->nr_pfns) {
+			unsigned long index = gfn - p->base_pfn;
+
+			return (p->pfns[index] & KVMPPC_UVMEM_SHARED);
+		}
+	}
+	return false;
+}
+
 unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
 {
 	struct kvm_memslots *slots;
@@ -256,9 +335,13 @@ unsigned long kvmppc_h_svm_init_done(struct kvm *kvm)
  * is HV side fault on these pages. Next we *get* these pages, forcing
  * fault on them, do fault time migration to replace the device PTEs in
  * QEMU page table with normal PTEs from newly allocated pages.
+ *
+ * if @purge_gfn is set, cleanup any information related to each of
+ * the GFNs associated with this memory slot.
  */
 void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *free,
-			     struct kvm *kvm, bool skip_page_out)
+			     struct kvm *kvm, bool skip_page_out,
+			     bool purge_gfn)
 {
 	int i;
 	struct kvmppc_uvmem_page_pvt *pvt;
@@ -269,11 +352,22 @@ void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *free,
 		struct page *uvmem_page;
 
 		mutex_lock(&kvm->arch.uvmem_lock);
+
+		if (purge_gfn) {
+			/*
+			 * cleanup the shared status of the GFN here.
+			 * Any device PFN associated with the GFN shall
+			 * be cleaned up later, in kvmppc_uvmem_page_free()
+			 * when the device PFN is actually disassociated
+			 * from the GFN.
+			 */
+			kvmppc_gfn_uvmem_shared(gfn, kvm, false);
+		}
+
 		if (!kvmppc_gfn_is_uvmem_pfn(gfn, kvm, &uvmem_pfn)) {
 			mutex_unlock(&kvm->arch.uvmem_lock);
 			continue;
 		}
-
 		uvmem_page = pfn_to_page(uvmem_pfn);
 		pvt = uvmem_page->zone_device_data;
 		pvt->skip_page_out = skip_page_out;
@@ -304,7 +398,7 @@ unsigned long kvmppc_h_svm_init_abort(struct kvm *kvm)
 	srcu_idx = srcu_read_lock(&kvm->srcu);
 
 	kvm_for_each_memslot(memslot, kvm_memslots(kvm))
-		kvmppc_uvmem_drop_pages(memslot, kvm, false);
+		kvmppc_uvmem_drop_pages(memslot, kvm, false, true);
 
 	srcu_read_unlock(&kvm->srcu, srcu_idx);
 
@@ -470,8 +564,11 @@ static unsigned long kvmppc_share_page(struct kvm *kvm, unsigned long gpa,
 		goto retry;
 	}
 
-	if (!uv_page_in(kvm->arch.lpid, pfn << page_shift, gpa, 0, page_shift))
+	if (!uv_page_in(kvm->arch.lpid, pfn << page_shift, gpa, 0,
+				page_shift)) {
+		kvmppc_gfn_uvmem_shared(gfn, kvm, true);
 		ret = H_SUCCESS;
+	}
 	kvm_release_pfn_clean(pfn);
 	mutex_unlock(&kvm->arch.uvmem_lock);
 out:
@@ -527,8 +624,10 @@ unsigned long kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa,
 		goto out_unlock;
 
 	if (!kvmppc_svm_page_in(vma, start, end, gpa, kvm, page_shift,
-				&downgrade))
+				&downgrade)) {
+		kvmppc_gfn_uvmem_shared(gfn, kvm, false);
 		ret = H_SUCCESS;
+	}
 out_unlock:
 	mutex_unlock(&kvm->arch.uvmem_lock);
 out:
-- 
1.8.3.1