[Qemu-devel] [RFC PATCH v3 3/3] fw/pci: Allocate IGD stolen memory

[Alex Williamson <alex.williamson@redhat.com>]

Intel IGD makes use of memory allocated and marked reserved by the
BIOS as a stolen memory range.  For the most part, guest drivers don't
make use of this, but our achilles heel is the vBIOS.  The vBIOS
programs the device to use the host stolen memory range and it's used
in the pre-boot environment.  Generally the guest won't have access to
the host stolen memory area, so these accesses either land in VM
memory or unassigned space and generate IOMMU faults.  By allocating
this range in SeaBIOS and programming it into the device, QEMU (via
vfio) can make sure this guest allocated stolen memory range is used
instead.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 src/fw/pciinit.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
index 92170d5..c1ad5d4 100644
--- a/src/fw/pciinit.c
+++ b/src/fw/pciinit.c
@@ -260,7 +260,7 @@ static void ich9_smbus_setup(struct pci_device *dev, void *arg)
 static void intel_igd_opregion_setup(struct pci_device *dev, void *arg)
 {
     struct romfile_s *file = romfile_find("etc/igd-opregion");
-    void *opregion;
+    void *opregion, *bdsm;
     u16 bdf = dev->bdf;
 
     if (!file || !file->size)
@@ -281,6 +281,17 @@ static void intel_igd_opregion_setup(struct pci_device *dev, void *arg)
 
     dprintf(1, "Intel IGD OpRegion enabled on %02x:%02x.%x\n",
             pci_bdf_to_bus(bdf), pci_bdf_to_dev(bdf), pci_bdf_to_fn(bdf));
+
+    bdsm = memalign_high(1024 * 1024, 1024 * 1024);
+    if (!bdsm) {
+        warn_noalloc();
+        return;
+    }
+
+    pci_config_writel(bdf, 0x5C, cpu_to_le32((u32)bdsm));
+
+    dprintf(1, "Allocated 1MB reserved memory for Intel IGD stolen memory at "
+            "0x%08x\n", (u32)bdsm);
 }
 
 static const struct pci_device_id pci_device_tbl[] = {