[PATCH v3 2/2] drm/i915/ttm: Failsafe migration blits

[Matthew Auld]

On Tue, 2 Nov 2021 at 16:39, Thomas Hellström
<thomas.hellstrom at linux.intel.com> wrote:
>
> If the initial fill blit or copy blit of an object fails, the old
> content of the data might be exposed and read as soon as either CPU- or
> GPU PTEs are set up to point at the pages.
>
> Intercept the blit fence with an async callback that checks the
> blit fence for errors and if there are errors performs an async cpu blit
> instead. If there is a failure to allocate the async dma_fence_work,
> allocate it on the stack and sync wait for the blit to complete.
>
> Add selftests that simulate gpu blit failures and failure to allocate
> the async dma_fence_work.
>
> A previous version of this pach used dma_fence_work, now that's
> opencoded which adds more code but might lower the latency
> somewhat in the common non-error case.
>
> v3:
> - Style fixes (Matthew Auld)
>
> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Reviewed-by: Matthew Auld <matthew.auld at intel.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c  | 322 +++++++++++++++---
>  drivers/gpu/drm/i915/gem/i915_gem_ttm_move.h  |   5 +
>  .../drm/i915/gem/selftests/i915_gem_migrate.c |  24 +-
>  3 files changed, 295 insertions(+), 56 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> index 0ed6b7f2b95f..b89672c547f8 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> @@ -18,6 +18,29 @@
>  #include "gt/intel_gt.h"
>  #include "gt/intel_migrate.h"
>
> +/**
> + * DOC: Selftest failure modes for failsafe migration:
> + *
> + * For fail_gpu_migration, the gpu blit scheduled is always a clear blit
> + * rather than a copy blit, and then we force the failure paths as if
> + * the blit fence returned an error.
> + *
> + * For fail_work_allocation we fail the kmalloc of the async worker, we
> + * sync the gpu blit. If it then fails, or fail_gpu_migration is set to
> + * true, then a memcpy operation is performed sync.
> + */
> +#ifdef CONFIG_DRM_I915_SELFTEST

When pushing maybe make this:

#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)

Which seems to be consistent with most of the other places.

> +static bool fail_gpu_migration;
> +static bool fail_work_allocation;
> +
> +void i915_ttm_migrate_set_failure_modes(bool gpu_migration,
> +                                       bool work_allocation)
> +{
> +       fail_gpu_migration = gpu_migration;
> +       fail_work_allocation = work_allocation;
> +}
> +#endif
> +