Re: [PATCH v7 2/7] kvmppc: Shared pages support for secure guests

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, the device page is
unmapped from the HV side page tables.

Signed-off-by: Bharata B Rao <redacted>
---
 arch/powerpc/include/asm/hvcall.h |  3 ++
 arch/powerpc/kvm/book3s_hv_devm.c | 70 +++++++++++++++++++++++++++++--
 2 files changed, 69 insertions(+), 4 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 13722f27fa7d..6a3229b78fed 100644
--- a/arch/powerpc/kvm/book3s_hv_devm.c
+++ b/arch/powerpc/kvm/book3s_hv_devm.c

@@ -46,6 +46,7 @@ struct kvmppc_devm_page_pvt {
 	unsigned long *rmap;
 	unsigned int lpid;
 	unsigned long gpa;
+	bool skip_page_out;
 };

 /*

@@ -139,6 +140,54 @@ 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 unmap the device page from QEMU's page tables.
+ */
+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_rmap_is_devm_pfn(*rmap)) {
+		devm_page = pfn_to_page(*rmap & ~KVMPPC_RMAP_DEVM_PFN);
+		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.
  */

@@ -159,9 +208,12 @@ 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);

@@ -211,7 +263,7 @@ kvmppc_devm_fault_migrate_alloc_and_copy(struct migrate_vma *mig,
 	struct page *dpage, *spage;
 	struct kvmppc_devm_page_pvt *pvt;
 	unsigned long pfn;
-	int ret;
+	int ret = U_SUCCESS;

 	spage = migrate_pfn_to_page(*mig->src);
 	if (!spage || !(*mig->src & MIGRATE_PFN_MIGRATE))

@@ -226,8 +278,18 @@ kvmppc_devm_fault_migrate_alloc_and_copy(struct migrate_vma *mig,
 	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: