[BUG] [Linux] Steam Link VR NVIDIA startup crash in `videovulkan::SetupEncoder()` quality-level query

[46cv8]

Describe the Bug

When connecting a Meta Quest 2 through Steam Link VR on Linux, SteamVR begins
initializing Valve's vrlink Vulkan video encoder, then vrserver segfaults
and the headset disconnects. The desktop displays:

SteamVR Graphics Error
You may need to update your computers graphics
(405)

I traced the crash in Valve's unmodified driver_vrlink.so to an indirect call
from videovulkan::SetupEncoder() through
vkGetPhysicalDeviceVideoEncodeQualityLevelPropertiesKHR. In the failing run,
that call dispatches through a null pointer.

A one-branch diagnostic bypass of the NVIDIA quality-level query path lets the
same system initialize Steam Link VR and reach SteamVR Home, including with
10-bit video enabled.

To Reproduce

1. Use Valve's unmodified SteamVR driver_vrlink.so.
2. Start SteamVR on the Linux host.
3. Start Steam Link VR on the Quest 2 and connect to the host.
4. Wait for headset/encoder initialization.

Expected Behavior

Steam Link VR should connect and enter SteamVR Home or another VR scene.

Actual Behavior

SteamVR displays error (405), the headset session disconnects, and vrserver
segfaults during driver_vrlink.so video encoder setup.

System Information

• Distribution: Ubuntu 22.04.5 LTS
• Kernel: 6.8.0-111-generic (#111~22.04.1-Ubuntu)
• GPU: NVIDIA GeForce RTX 3060
• NVIDIA driver: 595.71.05
• SteamVR version: 2.15.6
• SteamVR beta also tested: build shown by Steam as 23084509; same startup failure
• Steam client version: [fill in from Steam > Help > About Steam before submitting]
• Headset/client: Meta Quest 2, Steam Link VR (qvlclient;hollywood;2.0.22.2080)
• Connection type: wireless Steam Link VR
• Vulkan encode extensions reported by vulkaninfo:

VK_KHR_video_encode_h264
VK_KHR_video_encode_h265
VK_KHR_video_encode_intra_refresh
VK_KHR_video_encode_quantization_map
VK_KHR_video_encode_queue

Log Sequence Immediately Before the Crash

driver_vrlink.txt from the unmodified-driver run ends its encoder
initialization sequence with:

SVLRoot::SVLRoot() sReqEncMode = mid
SVLDataLink::InitCrypt() m_TransportMode = 1 // 1017
[HMDVulkan] Created VkDevice with Compute Queue Family: 2 and Video Encode Queue Family: 4.
[VideoVulkan] Init()
[VideoVulkan] Is 10 bit SUPPORTED? Yes
[VideoVulkan] Is Ultra Low Latency SUPPORTED? Yes
m_eChosenRateControlMode: 4
[VideoVulkan] Setting video capabilties: 10bit: No, ull: Yes

The resulting primary crash is:

CrashID=bp-be86bd8c-687a-4084-8043-606bd2260523
vrserver[53368]: segfault at 0 ip 0000000000000000
Exception=EXCEPTION_SIGSEGV
Module=driver_vrlink.so
Symbol=videovulkan::SetupEncoder()
Return address=driver_vrlink.so+0xba1b9

Disassembly at the Crash Site

The unmodified SteamVR 2.15.6 binary contains the following instruction
sequence at the failing call:

ba14f: lea    0xc7c6a2(%rip),%rax # d367f8 <vkGetPhysicalDeviceVideoEncodeQualityLevelPropertiesKHR>
ba1b0: mov    0x8(%rdx),%rdi
ba1b4: mov    %r8,%rdx
ba1b7: call   *(%rax)
ba1b9: test   %eax,%eax

The crash instruction pointer is 0x0, indicating that
call *(%rax) attempted to invoke a null
vkGetPhysicalDeviceVideoEncodeQualityLevelPropertiesKHR pointer.

I also repeated the startup test with Steam's Fossilize layer disabled. It
failed at the same driver_vrlink.so+0xba1b9 return address, so Fossilize is
not the cause of this initialization failure.

Diagnostic Binary Diff

I only have the shipped binary, not VRLink source. The following one-branch
binary change was used only to test whether the quality-level path is the
blocking failure:

 File offset:      0x000b9ba2
 Original SHA256:  1191bb8f8f63e5572888ee0dab5f4586b6394189ce5a26ee508521fd1875ea86

-0f 84 68 05 00 00    je videovulkan::SetupEncoder()+0x670   ; enter NVIDIA quality-level query path
+90 90 90 90 90 90    nop; nop; nop; nop; nop; nop            ; continue through normal video-session path

 Patched SHA256:   b3aaf53e91c6d6a1d2a714d72c88df61d89bd14b4f07c3c0fd4d572ea815c177

Result After the Diagnostic Bypass

With only that branch bypass applied, Steam Link VR passes its prior startup
crash and initializes successfully:

[VideoVulkan] Created vkCreateVideoSessionKHR! chosen m_MaxSVLVideoExtent: 3200x8192
[VideoVulkan] Init Success!
[HMDVulkan] Activate: Done!

I could then reach SteamVR Home on the Quest 2. With the SteamVR setting below,
10-bit initialization also succeeded:

"driver_vrlink": {
  "10bit": true
}

[VideoVulkan] Is 10 bit SUPPORTED? Yes
[VideoVulkan]    format: 1000156013
[VideoVulkan] Init Success!
[HMDVulkan] Activate: Done!

Suggested Code-Level Fix

driver_vrlink should verify that
vkGetPhysicalDeviceVideoEncodeQualityLevelPropertiesKHR has been loaded
before calling it. If the function is unavailable, setup appears capable of
continuing using its non-quality-level/default selection path.

Conceptually:

-result = vkGetPhysicalDeviceVideoEncodeQualityLevelPropertiesKHR(physical_device, &query, &properties);
-if (result == VK_SUCCESS) {
-    apply_quality_level_properties(properties);
-}
+if (vkGetPhysicalDeviceVideoEncodeQualityLevelPropertiesKHR != nullptr) {
+    result = vkGetPhysicalDeviceVideoEncodeQualityLevelPropertiesKHR(physical_device, &query, &properties);
+    if (result == VK_SUCCESS) {
+        apply_quality_level_properties(properties);
+    }
+} else {
+    use_default_encode_configuration();
+}

The actual source structure may differ; the important observable behavior is
that the quality-level query is entered with an invalid function pointer and
skipping that query allows encoder initialization to complete.

Related Public Tracker Context

• ValveSoftware/SteamVR-for-Linux#837 reported a broad Steam Link connection
  crash on Quest hardware and was closed on 2026-03-27 after its original
  reporter stated that it no longer reproduced. It may be related by symptom,
  but it does not identify this videovulkan::SetupEncoder() call site.
• I could not find public VRLink implementation source in
  ValveSoftware/SteamVR-for-Linux; the repository currently contains issue
  templates and diagnostics/documentation files rather than
  driver_vrlink.so source.

Attachments Available

• The unmodified-driver vrserver minidump associated with the CrashID above
• driver_vrlink.txt and vrserver.txt from the unmodified failing run
• driver_vrlink.txt and vrserver.txt from the successful diagnostic-bypass run
• Steam runtime diagnostics and SteamVR system report: [generate immediately before submitting]

Separate Follow-Up Observation

After the diagnostic bypass allowed SteamVR Home to run, launching a VR
application exposed a separate crash during SteamVR Home texture teardown in
SVLHMDDriverVulkan::GetTextureSize() from the submit thread. I am not
treating that as this issue's primary bug because it was observed only after
applying the diagnostic bypass and is distinct from the reproducible
unmodified-driver startup failure described above.

Forgive me for having the AI write this bug report but I'm sure your AI can fix the code if it listens to my AI ;)

[Packetdancer]

There have been some reports of weird behavior with the Nvidia 595 proprietary driver, so it would be useful to test with version 580 just for comparison's sake.

In addition, you say 'attachments available' but did not include the attachments. Those logfiles would be useful, as driver_vrlink.txt in particular includes quite a bit about the overall initialization, and will make it more obvious if anything's going wrong. (Albeit only in the beta builds, so it would be best to generate the logs with the 2.16.5 beta.)

Also, fwiw, the AI summary isn't useful; it just sort of makes the bug overly verbose without necessarily adding much.

[46cv8]

I think the part about "vkGetPhysicalDeviceVideoEncodeQualityLevelPropertiesKHR" is pretty clear, I ran into other issues with steamlink crashing later on due to what turned out to be network issues but before I figured that out I had already switched to ALVR in the end. I'll try to dig up the driver_vrlink.txt files. Also I think it was crashing with 580 drivers for a different reason something related to some codec initialization errors (I don't have the logs for that). That was resolved by updating to the nvidia 595 drivers.

original_driver_vrlink.txt
patched_driver_vrlink.txt

Unfortunately right now I can't reinstall steamvr beta drivers and I also can't downgrade my nvidia drivers. If the data as is in this ticket isn't actionable, just close it.