[PATCH v4 4/6] xen/igd: enable guest creation when ROM read fails

For newer IGD devices, the host option ROM is not readable from sysfs
and this results in a call to error_fail() that causes Qemu to
exit(1) so guest creation fails with the current implementation for
many newer IGD devices. But this read failure need not be a fatal
error causing guest creation to fail because the guest does not need
the option ROM to successfully boot and run. The guest only needs the
option ROM for getting graphics output from the guest during early
boot before the guest OS loads the Intel IGD graphics drivers.

To fix this, allow guest creation to continue by avoiding setting errp
if the attempt to read the host ROM file from sysfs fails. In this case,
the memory for the guest option ROM has been allocated so free that
memory by calling object_unparent(OBJECT(&s->dev.rom)) before
continuing.

Replace the error_report() and error_printf() messages for this case
when the option ROM cannot be read via sysfs with a suitable
info_report() message.

In the case when the host option ROM cannot be read via the sysfs
interface, xen_pt_register_regions() will attempt to setup the option
ROM for the guest the same way it would for any other Xen passthrough
PCI device that has an option ROM.

Signed-off-by: Chuck Zmudzinski <[email protected]>
---
Changes in v4:
  - v4 is the first version of the series that has this patch

This patch provides initial support for many newer Intel IGD devices
so, at least, guest creation will not fail if such newer Intel
IGD devices are passed through to a Xen HVM guest. But this patch
alone is not sufficient for proper operation of the Intel IGD
for many, if not all, of the newer Intel IGD devices when passed
through to a Xen HVM guest.

There are two main problems with more recent, modern devices:

1. The newer divices might require patches to the Intel OpRegion
   and also an extended video bios table (VBT). Without support
   for these aspects of the newer devices, the experience will
   not be great and in many cases the Intel IGD still will not
   function properly in the guest.

2. The newer devices only work with UEFI AFAICT, and the Ovmf*
   platforms provided by the upsream edk2 project do not provide
   support for the Intel IGD. It appears the problem is that the
   ekd2 project deems the fact that the hardware manufacturer does
   not provide the necessary firmware, the EFI graphics output
   protocol (GOP) driver, in the ordinary way by making the EFI
   GOP driver accessible in virtual environments via the option
   ROM of the real PCI device, to be a reason to reject patches
   that add support for the Intel IGD. This, however, is not a
   fatal problem since it only affects the guest during early boot
   when OVMF or the bootloader is running and the guest OS
   graphics drivers have not yet been loaded. Lack of support
   for the Intel IGD in OVMF does not seem to affect the experience
   negatively once the guest OS graphics drivers have been loaded.
   So efforts to address this problem are only important in cases
   when it is necessary to get graphics output from OVMF and/or
   the guest bootloader.

The next two patches in this patchset address these two problems.
Of those two patches, the first one is more necessary, and the
second of those two patches is only needed to provide graphics output
from the guest during early boot.

 hw/xen/xen_pt_graphics.c | 7 +++++++
 hw/xen/xen_pt_load_rom.c | 5 +----
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/hw/xen/xen_pt_graphics.c b/hw/xen/xen_pt_graphics.c
index 0ae95cc..a124233 100644
--- a/hw/xen/xen_pt_graphics.c
+++ b/hw/xen/xen_pt_graphics.c
@@ -187,6 +187,13 @@ void xen_pt_setup_vga(XenPCIPassthroughState *s, XenHostPCIDevice *dev,
         return;
     }
 
+    /* Case when the host ROM file from sysfs could not be read */
+    if (!bios_size) {
+        object_unparent(OBJECT(&s->dev.rom));
+        bios = NULL;
+        return;
+    }
+
     if (bios_size < sizeof(struct rom_header)) {
         error_setg(errp, "VGA: VBIOS image corrupt (too small)");
         return;
diff --git a/hw/xen/xen_pt_load_rom.c b/hw/xen/xen_pt_load_rom.c
index 407b630..eaf0ae1 100644
--- a/hw/xen/xen_pt_load_rom.c
+++ b/hw/xen/xen_pt_load_rom.c
@@ -77,10 +77,7 @@ void *pci_assign_dev_load_option_rom(PCIDevice *dev,
     memset(ptr, 0xff, dev->romsize);
 
     if (!fread(ptr, 1, st.st_size, fp)) {
-        error_report("pci-assign: Cannot read from host %s", rom_file);
-        error_printf("Device option ROM contents are probably invalid "
-                     "(check dmesg).\nSkip option ROM probe with rombar=0, "
-                     "or load from file with romfile=\n");
+        info_report("pci-assign: Cannot read Option ROM %s from host", rom_file);
         goto close_rom;
     }
 
-- 
2.52.0