drm/i915/gvt: protect RO and Rsvd bits of virtual vgpu configuration space

Per PCI specification, Configuration Register has different types (RO,
RW, RW1C, Rsvd). For RO Register bits are read-only and cannot be
altered by software. For RW1C Register bits indicate status when read.
A Set bit indicates a status event which is Cleared by writing a 1b.
Writing a 0b to RW1C bits has no effect. Reserved Register is for future
implementations, and they are read-only and must return zero when read.

Current vGPU configuration write emulation just copy the value as it is.
So we haven't emulated RO, RW1C and Rsvd Registers correctly. This patch
is following the Spec to correct emulation logic. We add a function
vgpu_cfg_mem_write to wrap the access to vGPU configuration memory.
The write function uses a RW Register bitmap to avoid RO bits be
overwritten, and emulate RW1C behavior for the particular status Register.

v2:
  new = src[i] --> new = src[i] & mask (zhenyu)

Signed-off-by: Changbin Du <changbin.du@intel.com>
Cc: Xiaoguang Chen <xiaoguang.chen@intel.com>
Cc: Zhiyuan Lv <zhiyuan.lv@intel.com>
Cc: Min He <min.he@intel.com>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/cfg_space.c

@@ -41,6 +41,54 @@ enum {
 	INTEL_GVT_PCI_BAR_MAX,
 };
 
+/* bitmap for writable bits (RW or RW1C bits, but cannot co-exist in one
+ * byte) byte by byte in standard pci configuration space. (not the full
+ * 256 bytes.)
+ */
+static const u8 pci_cfg_space_rw_bmp[PCI_INTERRUPT_LINE + 4] = {
+	[PCI_COMMAND]		= 0xff, 0x07,
+	[PCI_STATUS]		= 0x00, 0xf9, /* the only one RW1C byte */
+	[PCI_CACHE_LINE_SIZE]	= 0xff,
+	[PCI_BASE_ADDRESS_0 ... PCI_CARDBUS_CIS - 1] = 0xff,
+	[PCI_ROM_ADDRESS]	= 0x01, 0xf8, 0xff, 0xff,
+	[PCI_INTERRUPT_LINE]	= 0xff,
+};
+
+/**
+ * vgpu_pci_cfg_mem_write - write virtual cfg space memory
+ *
+ * Use this function to write virtual cfg space memory.
+ * For standard cfg space, only RW bits can be changed,
+ * and we emulates the RW1C behavior of PCI_STATUS register.
+ */
+static void vgpu_pci_cfg_mem_write(struct intel_vgpu *vgpu, unsigned int off,
+				   u8 *src, unsigned int bytes)
+{
+	u8 *cfg_base = vgpu_cfg_space(vgpu);
+	u8 mask, new, old;
+	int i = 0;
+
+	for (; i < bytes && (off + i < sizeof(pci_cfg_space_rw_bmp)); i++) {
+		mask = pci_cfg_space_rw_bmp[off + i];
+		old = cfg_base[off + i];
+		new = src[i] & mask;
+
+		/**
+		 * The PCI_STATUS high byte has RW1C bits, here
+		 * emulates clear by writing 1 for these bits.
+		 * Writing a 0b to RW1C bits has no effect.
+		 */
+		if (off + i == PCI_STATUS + 1)
+			new = (~new & old) & mask;
+
+		cfg_base[off + i] = (old & ~mask) | new;
+	}
+
+	/* For other configuration space directly copy as it is. */
+	if (i < bytes)
+		memcpy(cfg_base + off + i, src + i, bytes - i);
+}
+
 /**
  * intel_vgpu_emulate_cfg_read - emulate vGPU configuration space read
  *
@@ -123,7 +171,7 @@ static int emulate_pci_command_write(struct intel_vgpu *vgpu,
 	u8 changed = old ^ new;
 	int ret;
 
-	memcpy(vgpu_cfg_space(vgpu) + offset, p_data, bytes);
+	vgpu_pci_cfg_mem_write(vgpu, offset, p_data, bytes);
 	if (!(changed & PCI_COMMAND_MEMORY))
 		return 0;
 
@@ -277,10 +325,10 @@ int intel_vgpu_emulate_cfg_write(struct intel_vgpu *vgpu, unsigned int offset,
 		if (ret)
 			return ret;
 
-		memcpy(vgpu_cfg_space(vgpu) + offset, p_data, bytes);
+		vgpu_pci_cfg_mem_write(vgpu, offset, p_data, bytes);
 		break;
 	default:
-		memcpy(vgpu_cfg_space(vgpu) + offset, p_data, bytes);
+		vgpu_pci_cfg_mem_write(vgpu, offset, p_data, bytes);
 		break;
 	}
 	return 0;