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

[Matthew Auld]

On Tue, 2 Nov 2021 at 17:55, Thomas Hellström
<thomas.hellstrom at linux.intel.com> wrote:
>
>
> On 11/2/21 18:40, Matthew Auld wrote:
> > 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.
>
> Hmm,
>
> I noticed that i915 is doing that, although I thought these macros were
> primarily intended for C expressions?

i915 is not the only one. AFAIK it just conveniently handles both
bultin and module.

>
> /Thomas
>
>
> >
> >> +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
> >> +