[PATCH v6 2/7] kvmppc: Shared pages support for secure guests

[Bharata B Rao <bharata@linux.ibm.com>]

A secure guest will share some of its pages with hypervisor (Eg. virtio
bounce buffers etc). Support sharing of pages between hypervisor and
ultravisor.

Once a secure page is converted to shared page, stop tracking that page
as a device page.

Signed-off-by: Bharata B Rao <bharata@linux.ibm.com>
---
 arch/powerpc/include/asm/hvcall.h |  3 ++
 arch/powerpc/kvm/book3s_hv_devm.c | 67 +++++++++++++++++++++++++++++--
 2 files changed, 67 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/hvcall.h b/arch/powerpc/include/asm/hvcall.h
index 2f6b952deb0f..05b8536f6653 100644
--- a/arch/powerpc/include/asm/hvcall.h
+++ b/arch/powerpc/include/asm/hvcall.h
@@ -337,6 +337,9 @@
 #define H_TLB_INVALIDATE	0xF808
 #define H_COPY_TOFROM_GUEST	0xF80C
 
+/* Flags for H_SVM_PAGE_IN */
+#define H_PAGE_IN_SHARED        0x1
+
 /* Platform-specific hcalls used by the Ultravisor */
 #define H_SVM_PAGE_IN		0xEF00
 #define H_SVM_PAGE_OUT		0xEF04
diff --git a/arch/powerpc/kvm/book3s_hv_devm.c b/arch/powerpc/kvm/book3s_hv_devm.c
index 2e6c077bd22e..c9189e58401d 100644
--- a/arch/powerpc/kvm/book3s_hv_devm.c
+++ b/arch/powerpc/kvm/book3s_hv_devm.c
@@ -55,6 +55,7 @@ struct kvmppc_devm_page_pvt {
 	unsigned long *rmap;
 	unsigned int lpid;
 	unsigned long gpa;
+	bool skip_page_out;
 };
 
 struct kvmppc_devm_copy_args {
@@ -188,6 +189,54 @@ kvmppc_devm_migrate_alloc_and_copy(struct migrate_vma *mig,
 	return 0;
 }
 
+/*
+ * Shares the page with HV, thus making it a normal page.
+ *
+ * - If the page is already secure, then provision a new page and share
+ * - If the page is a normal page, share the existing page
+ *
+ * In the former case, uses the dev_pagemap_ops migrate_to_ram handler to
+ * release the device page.
+ */
+static unsigned long
+kvmppc_share_page(struct kvm *kvm, unsigned long gpa, unsigned long page_shift)
+{
+
+	int ret = H_PARAMETER;
+	struct page *devm_page;
+	struct kvmppc_devm_page_pvt *pvt;
+	unsigned long pfn;
+	unsigned long *rmap;
+	struct kvm_memory_slot *slot;
+	unsigned long gfn = gpa >> page_shift;
+	int srcu_idx;
+
+	srcu_idx = srcu_read_lock(&kvm->srcu);
+	slot = gfn_to_memslot(kvm, gfn);
+	if (!slot)
+		goto out;
+
+	rmap = &slot->arch.rmap[gfn - slot->base_gfn];
+	if (kvmppc_is_devm_pfn(*rmap)) {
+		devm_page = pfn_to_page(*rmap & ~KVMPPC_PFN_DEVM);
+		pvt = (struct kvmppc_devm_page_pvt *)
+			devm_page->zone_device_data;
+		pvt->skip_page_out = true;
+	}
+
+	pfn = gfn_to_pfn(kvm, gpa >> page_shift);
+	if (is_error_noslot_pfn(pfn))
+		goto out;
+
+	ret = uv_page_in(kvm->arch.lpid, pfn << page_shift, gpa, 0, page_shift);
+	if (ret = U_SUCCESS)
+		ret = H_SUCCESS;
+	kvm_release_pfn_clean(pfn);
+out:
+	srcu_read_unlock(&kvm->srcu, srcu_idx);
+	return ret;
+}
+
 /*
  * Move page from normal memory to secure memory.
  */
@@ -209,9 +258,12 @@ kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa,
 	if (page_shift != PAGE_SHIFT)
 		return H_P3;
 
-	if (flags)
+	if (flags & ~H_PAGE_IN_SHARED)
 		return H_P2;
 
+	if (flags & H_PAGE_IN_SHARED)
+		return kvmppc_share_page(kvm, gpa, page_shift);
+
 	ret = H_PARAMETER;
 	down_read(&kvm->mm->mmap_sem);
 	srcu_idx = srcu_read_lock(&kvm->srcu);
@@ -279,8 +331,17 @@ kvmppc_devm_fault_migrate_alloc_and_copy(struct migrate_vma *mig)
 	pvt = (struct kvmppc_devm_page_pvt *)spage->zone_device_data;
 
 	pfn = page_to_pfn(dpage);
-	ret = uv_page_out(pvt->lpid, pfn << PAGE_SHIFT,
-			  pvt->gpa, 0, PAGE_SHIFT);
+
+	/*
+	 * This same function is used in two cases:
+	 * - When HV touches a secure page, for which we do page-out
+	 * - When a secure page is converted to shared page, we touch
+	 *   the page to essentially discard the device page. In this
+	 *   case we skip page-out.
+	 */
+	if (!pvt->skip_page_out)
+		ret = uv_page_out(pvt->lpid, pfn << PAGE_SHIFT,
+				  pvt->gpa, 0, PAGE_SHIFT);
 	if (ret = U_SUCCESS)
 		*mig->dst = migrate_pfn(pfn) | MIGRATE_PFN_LOCKED;
 	return 0;
-- 
2.21.0