mxgrub: Unload NVIDIA driver before kexec reboot

mxgrub/mxgrub

@@ -373,10 +373,27 @@ sub cmd_initramfs {
 	sys('bash','-c','cd /project/admin/initramfs ; find . -name ".git*" -prune -or -print | cpio -H newc -o | gzip > /boot/grub/initramfs.igz');
 }
 
+# NVIDIA GSP-based GPUs (e.g. A100) are not reset by kexec: the GSP and its
+# WPR2 carveout survive into the next kernel, whose freshly-initialised IOMMU
+# then rejects the stale DMA (AMD-Vi IO_PAGE_FAULT), the GSP faults (Xid 120),
+# and the driver cannot re-init (RmInitAdapter 0x62 = NV_ERR_RESET_REQUIRED),
+# so nvidia-smi reports "No devices were found". Unloading the driver first
+# lets it shut the GSP down cleanly so the next kernel enumerates a healthy
+# GPU. Best effort: if a module is absent or busy, proceed with the reboot
+# anyway (no worse than not unloading at all).
+sub quiesce_nvidia {
+	return if system('lsmod | grep -q "^nvidia "');	# no NVIDIA driver loaded
+	warn "mxgrub: unloading NVIDIA driver before kexec ...\n";
+	for my $mod (qw(nvidia_drm nvidia_modeset nvidia_uvm nvidia)) {
+		system('rmmod',$mod);	# ignore failures (not loaded / in use)
+	}
+}
+
 sub cmd_reboot {
 	my $chosen=get_chosen();
 	my $image=label_to_image($chosen);
 	-e "/boot/$image" or die "/boot/$image: no such file\n";
+	quiesce_nvidia();
 	sys('sync');
 	sys('kexec',"/boot/$image",'--initrd=/boot/grub/initramfs.igz',"--command-line=root=LABEL=root $KERNEL_PARAMETER");
 }