[RFC v2 14/19] KVM: arm64: ITS: Add infrastructure for table lookup

[Eric Auger <eric.auger@redhat.com>]

Add a generic lookup_table() helper whose role consists in
scanning a contiguous table located in guest RAM and applying
a callback on each entry. Entries can be handled as linked lists
since the callback may return an offset to the next entry and
also tell that an entry is the last one.

Helper functions also are added to compute the device/event ID
offset to the next DTE/ITE.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
---
 virt/kvm/arm/vgic/vgic-its.c | 119 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)

diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
index 1cd6ae6..cf04776 100644
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -181,6 +181,8 @@ static struct its_ite *find_ite(struct vgic_its *its, u32 device_id,
 #define VITS_ESZ 8
 #define VITS_TYPER_IDBITS 0xF
 #define VITS_TYPER_DEVBITS 0xF
+#define VITS_DTE_MAX_DEVID_OFFSET GENMASK(19, 0)
+#define VITS_ITE_MAX_EVENTID_OFFSET GENMASK(16, 0)
 
 /*
  * Finds and returns a collection in the ITS collection table.
@@ -1607,6 +1609,123 @@ int vgic_its_attr_regs_access(struct kvm_device *dev,
 	return 0;
 }
 
+static u32 compute_next_devid_offset(struct list_head *h,
+				     struct its_device *dev)
+{
+	struct list_head *e = &dev->dev_list;
+	struct its_device *next;
+	u32 next_offset;
+
+	if (e->next == h)
+		return 0;
+	next = list_entry(e->next, struct its_device, dev_list);
+	next_offset = next->device_id - dev->device_id;
+
+	return next_offset < VITS_DTE_MAX_DEVID_OFFSET ?
+			next_offset : VITS_DTE_MAX_DEVID_OFFSET;
+}
+
+static u32 compute_next_eventid_offset(struct list_head *h,
+				       struct its_ite *ite)
+{
+	struct list_head *e = &ite->ite_list;
+	struct its_ite *next;
+	u32 next_offset;
+
+	if (e->next == h)
+		return 0;
+	next = list_entry(e->next, struct its_ite, ite_list);
+	next_offset = next->event_id - ite->event_id;
+
+	return next_offset < VITS_ITE_MAX_EVENTID_OFFSET ?
+			next_offset : VITS_ITE_MAX_EVENTID_OFFSET;
+}
+
+static int next_segment(unsigned long len, int offset)
+{
+	if (len > PAGE_SIZE - offset)
+		return PAGE_SIZE - offset;
+	else
+		return len;
+}
+
+/**
+ * entry_fn_t - Callback called on a table entry restore path
+ * @its: its handle
+ * @id: id of the entry
+ * @addr: kernel VA of the entry
+ * @opaque: pointer to an opaque data
+ * @next_offset: minimal ID offset to the next entry. 0 if this
+ * entry is the last one, 1 if the entry is invalid, >= 1 if an
+ * entry's next_offset field was truly decoded
+ *
+ * Return: < 0 on error, 0 otherwise
+ */
+typedef int (*entry_fn_t)(struct vgic_its *its, u32 id, void *addr,
+			  void *opaque, u32 *next_offset);
+
+/**
+ * lookup_table - scans a contiguous table in guest RAM and applies a function
+ * to each entry
+ *
+ * @its: its handle
+ * @base: base gpa of the table
+ * @size: size of the table in bytes
+ * @esz: entry size in bytes
+ * @start_id: first entry's ID
+ * @fn: function to apply on each entry
+ *
+ * Return: < 0 on error, 1 if last element identified, 0 otherwise
+ */
+static int lookup_table(struct vgic_its *its, gpa_t base, int size, int esz,
+			int start_id, entry_fn_t fn, void *opaque)
+{
+	gpa_t gpa = base, top = base + size - 1;
+	unsigned long len = top - gpa;
+	int ret, seg, offset = offset_in_page(gpa);
+	gfn_t gfn = gpa >> PAGE_SHIFT;
+	u32 id = start_id + (gpa - base)/esz;
+	struct kvm *kvm = its->dev->kvm;
+	kvm_pfn_t pfn;
+
+	while ((seg = next_segment(len, offset)) != 0) {
+		u32 next_offset;
+		bool writeable;
+		void *addr;
+
+		pfn = gfn_to_pfn_prot(kvm, gfn, true, &writeable);
+		if (is_error_noslot_pfn(pfn))
+			return -EINVAL;
+		addr = phys_to_virt((u64)pfn << PAGE_SHIFT);
+		addr += offset;
+
+		while (seg > 0) {
+			size_t byte_offset;
+
+			ret = fn(its, id, addr, opaque, &next_offset);
+			if (ret < 0 || (!ret && !next_offset))
+				goto out;
+
+			byte_offset = next_offset * esz;
+
+			id += next_offset;
+			gpa += byte_offset;
+			addr += byte_offset;
+			seg -= byte_offset;
+		}
+		kvm_release_pfn_clean(pfn);
+
+		len = top - gpa;
+		offset = offset_in_page(gpa);
+		gfn = gpa >> PAGE_SHIFT;
+		id = start_id + (gpa - base)/esz;
+	}
+	return 0;
+out:
+	kvm_release_pfn_clean(pfn);
+	return (ret < 0 ? ret : 1);
+}
+
 /**
  * vgic_its_flush_pending_tables - Flush the pending tables into guest RAM
  */
-- 
2.5.5