xen/x86: obtain upper 32 bits of video frame buffer address for Dom0

The hypervisor has been supplying this information for a couple of major
releases. Make use of it. The need to set a flag in the capabilities
field also points out that the prior setting of that field from the
hypervisor interface's gbl_caps one was wrong, so that code gets deleted
(there's also no equivalent of this in native boot code).

Signed-off-by: Jan Beulich <[e-mail]>
Reviewed-by: Boris Ostrovsky <[e-mail]>

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Juergen Gross <[e-mail]>

arch/x86/xen/vga.c

···
 		}
 
 		if (size >= offsetof(struct dom0_vga_console_info,
-				     u.vesa_lfb.gbl_caps)
-		    + sizeof(info->u.vesa_lfb.gbl_caps))
-			screen_info->capabilities = info->u.vesa_lfb.gbl_caps;
-		if (size >= offsetof(struct dom0_vga_console_info,
 				     u.vesa_lfb.mode_attrs)
 		    + sizeof(info->u.vesa_lfb.mode_attrs))
 			screen_info->vesa_attributes = info->u.vesa_lfb.mode_attrs;
+
+		if (size >= offsetof(struct dom0_vga_console_info,
+				     u.vesa_lfb.ext_lfb_base)
+		    + sizeof(info->u.vesa_lfb.ext_lfb_base)
+		    && info->u.vesa_lfb.ext_lfb_base) {
+			screen_info->ext_lfb_base = info->u.vesa_lfb.ext_lfb_base;
+			screen_info->capabilities |= VIDEO_CAPABILITY_64BIT_BASE;
+		}
 		break;
 	}
 }

include/xen/interface/xen.h

···
 			uint32_t gbl_caps;
 			/* Mode attributes (offset 0x0, VESA command 0x4f01). */
 			uint16_t mode_attrs;
+			uint16_t pad;
+			/* high 32 bits of lfb_base */
+			uint32_t ext_lfb_base;
 		} vesa_lfb;
 	} u;
 };