Re: [RFC PATCH v3 0/1] drm/amdgpu: MMIO TLB invalidation fallback when KIQ is wedged after S4 resume

[Alex Deucher]

On Mon, Aug 24, 2026 at 12:30 PM Denis Pisarev <pisarevden@xxxxxxxxx> wrote:
>
> Hi,
>
> v3 addresses the two findings from the sashiko-bot review of v2.
> Failure data and trigger isolation are unchanged (bugzilla 219492):
> S4 resume on Cezanne (gmc_v9, GFXOFF) wedges KIQ TLB flushes at
> 80-140/hour for 9+ hours with sched.ready true throughout; holding
> GFXOFF off across the S4 cycle produces zero errors.
>
> 1. [High] "VFs and interrupt contexts silently drop TLB flushes once
>    the threshold is reached" - correct, and fixed. In v3 the latch
>    only reroutes bare metal process context to MMIO. VFs and IRQ
>    contexts keep submitting to KIQ exactly as before this patch, with
>    per-failure logging, because they have no MMIO alternative; there
>    is no longer any code path that drops a flush without attempting
>    and logging.
>
> 2. [High] "KIQ and MMIO race on the same invalidation engine if KIQ
>    recovers" - this remains the documented open question; no code
>    change in v3. Our analysis: once latched, this path submits no new
>    KIQ commands, so the exposure is limited to already-queued stale
>    commands and the recovery transition window. The engine serializes
>    requests internally, so the realistic worst case is a lost flush
>    request caught by the existing ACK timeout ("Timeout waiting for VM
>    flush ACK!"), not silent state corruption. If maintainers consider
>    a fence necessary (or a dedicated invalidate engine for the MMIO
>    path), guidance on the preferred mechanism would be welcome.
>
> Full patch history: v1 (initial fallback+counter), v2 (GFXOFF hold,
> per-instance counter, irqsave, VF/IRQ restrictions, MES error
> propagation) - all from bot review; v3 (this one) fixes the VF/IRQ
> drop regression the bot found in v2.
>
> Also still open from the cover letters: the alternative direction of
> fixing the S4 resume ordering itself (RLC/ME vs GFXOFF) instead of a
> runtime fallback. Happy to run tracing on the affected hardware.
>

If that's a problem, that should be fixed.  That said, did you have
any success with the branch I proposed?

Alex

> Patch 1/1 follows.
>
> Denis Pisarev
>
> Denis Pisarev (1):
>   drm/amdgpu: fall back to MMIO TLB invalidation when KIQ is
>     unresponsive
>
>  drivers/gpu/drm/amd/amdgpu/amdgpu.h     |   2 +
>  drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.h |   2 +
>  drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c |  18 ++--
>  drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h |   2 +-
>  drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c   | 123 +++++++++++++++++++-----
>  5 files changed, 114 insertions(+), 33 deletions(-)
>
> --
> 2.55.0
>