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feat(vdisplay/driver): the frame pump survives MMCSS refusal and outranks GPU contention

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Two stall-immunity hardenings for the swap-chain drain thread (branch-2 of the
disturbance-immunity program — failures in OUR delivery leg, as opposed to
adapter-wide display servicing, which no priority survives):

- MMCSS registration fails under the restricted WUDFHost token on some boxes;
  the drain thread then ran UNPRIORITIZED — the whole display's frame pump at
  normal priority, starvable by DDC/HPD-servicing DPC pressure into
  multi-hundred-ms delivery holes. Fall back to TIME_CRITICAL.

- IddCxSetRealtimeGPUPriority (IddCx 1.9) raises the processing device above
  every regular application's GPU priority. Slot availability comes from
  raising the exported IddMinimumVersionRequired 4 → 10, which was overdue
  independently: the drain loop already calls ReleaseAndAcquireBuffer2 (1.10)
  unconditionally, so binding a pre-1.10 framework would dispatch past the
  populated IddFunctions table — with 10 an old framework fails the bind
  cleanly instead. The product floor is already Win11 22H2 (installer
  MinVersion=10.0.22621, whose framework is 1.10), so no supported system
  changes behavior.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
enricobuehler
2026-07-27 15:24:10 +02:00
co-authored by Claude Fable 5
parent 94f0207cbd
commit 19d6f79d2d
3 changed files with 70 additions and 7 deletions
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packaging/windows/drivers/pf-vdisplay/src/lib.rs
+11 -2
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@@ -41,6 +41,15 @@ pub(crate) const STATUS_BUFFER_TOO_SMALL: NTSTATUS = 0xC000_0023u32 as NTSTATUS;
/// IddCx (stub mode) requires the driver to export the minimum IddCx framework version it needs — the
/// `#ifndef IDD_STUB` branch of `IddCxFuncEnum.h` that normally emits it is compiled out under
/// `IDD_STUB`. `4` matches the proven `wdf-umdf` oracle.
/// `IDD_STUB`.
///
/// `10` = IddCx 1.10, the TRUTHFUL floor: the drain loop calls
/// `IddCxSwapChainReleaseAndAcquireBuffer2` (1.10) unconditionally and the swap-chain worker uses
/// `IddCxSetRealtimeGPUPriority` (1.9); the product floor is already Windows 11 22H2 / build 22621,
/// whose framework is 1.10 (the installer gate — `MinVersion=10.0.22621` in punktfunk-host.iss —
/// exists precisely for this driver). The oracle's historical `4` predated that floor and would let
/// the driver load against a SHORT `IddFunctions` table, where dispatching any post-1.4 DDI reads
/// past the populated entries. With `10`, an older framework fails the bind cleanly (driver doesn't
/// load) instead of limping into undefined dispatch.
#[unsafe(no_mangle)]
pub static IddMinimumVersionRequired: wdk_sys::ULONG = 4;
pub static IddMinimumVersionRequired: wdk_sys::ULONG = 10;