fix(os/image): enable MMCONFIG so Blackwell GPUs can be probed

os/image/kernel-cmdline.sh

@@ -13,14 +13,31 @@
 # one would have produced measurements describing a command line the guest
 # never booted with -- and every existing check would still have passed.
 
+# `pci=nommconf` is deliberately absent. It confines PCI config space access to
+# the legacy CF8h/CFCh port I/O path, which physically cannot reach past the
+# first 256 bytes, so `pci_find_ext_capability()` short-circuits on
+# `dev->cfg_size <= PCI_CFG_SPACE_SIZE` and the whole PCIe extended config space
+# (offset >= 0x100) becomes unreadable. Blackwell GPU drivers walk that space to
+# find NVIDIA's vendor DVSEC; with MMCONFIG off the reads return 0xFFFFFFFF, the
+# driver asserts on every probe, and every later cuInit() fails with
+# CUDA_ERROR_SYSTEM_NOT_READY (802). There is no substitute mechanism, so GPU
+# passthrough requires MMCONFIG.
+#
+# `pci=noearly` is kept. It gates a different mechanism -- early type 1 scanning,
+# which runs before ACPI is parsed and dispatches into vendor fixups keyed on the
+# vendor/device/class triple read straight out of a host-controlled config space.
+# GPU drivers bind during normal PCI enumeration and do not depend on it, and
+# Intel's confidential-computing guest hardening names early PCI code as
+# something to disable, so it stays off.
+
 # Emit the guest kernel command line.
 #   $1 dm-verity root hash
 #   $2 rootfs data size in bytes
 dstack_kernel_cmdline() {
     local root_hash=${1:?root hash required}
     local data_size=${2:?data size required}
     echo "console=ttyS0 init=/init panic=1 net.ifnames=0 biosdevname=0" \
-         "mce=off oops=panic pci=noearly pci=nommconf random.trust_cpu=y" \
+         "mce=off oops=panic pci=noearly random.trust_cpu=y" \
          "random.trust_bootloader=n tsc=reliable no-kvmclock" \
          "dstack.rootfs_hash=$root_hash dstack.rootfs_size=$data_size"
 }

os/yocto/layers/meta-dstack/recipes-core/images/dstack-uki.bb

@@ -22,8 +22,11 @@ KERNEL_IMAGETYPE = "bzImage"
 # Do NOT embed per-app dstack.mr_config_id here: AWS app/config binding is
 # measured from the shared-disk MrConfigV3 into NitroTPM PCR8 at guest setup,
 # so the UKI/AMI stays app-independent (PCR4 is OS-only).
+# Keep in sync with dstack_kernel_cmdline() in os/image/kernel-cmdline.sh, which
+# documents why pci=nommconf is absent (Blackwell needs PCIe extended config
+# space) and why pci=noearly stays.
 UKI_CMDLINE_BASE = "console=ttyS0 init=/init panic=1 net.ifnames=0 biosdevname=0 \
-mce=off oops=panic pci=noearly pci=nommconf random.trust_cpu=y random.trust_bootloader=n \
+mce=off oops=panic pci=noearly random.trust_cpu=y random.trust_bootloader=n \
 tsc=reliable no-kvmclock"
 
 # Flavor settings (should match dstack-rootfs.bb, set via multiconfig)