[Intel-gfx] [PATCH] i915: Drop relocation support on all new hardware (v3)

[Matthew Auld]

On 11/03/2021 08:14, Lucas De Marchi wrote:
> On Wed, Mar 10, 2021 at 1:50 PM Jason Ekstrand <jason at jlekstrand.net> wrote:
>>
>> The Vulkan driver in Mesa for Intel hardware never uses relocations if
>> it's running on a version of i915 that supports at least softpin which
>> all versions of i915 supporting Gen12 do.  On the OpenGL side, Gen12+ is
>> only supported by iris which never uses relocations.  The older i965
>> driver in Mesa does use relocations but it only supports Intel hardware
>> through Gen11 and has been deprecated for all hardware Gen9+.  The
>> compute driver also never uses relocations.  This only leaves the media
>> driver which is supposed to be switching to softpin going forward.
>> Making softpin a requirement for all future hardware seems reasonable.
>>
>> Rejecting relocations starting with Gen12 has the benefit that we don't
>> have to bother supporting it on platforms with local memory.  Given how
>> much CPU touching of memory is required for relocations, not having to
>> do so on platforms where not all memory is directly CPU-accessible
>> carries significant advantages.
>>
>> v2 (Jason Ekstrand):
>>   - Allow TGL-LP platforms as they've already shipped
>>
>> v3 (Jason Ekstrand):
>>   - WARN_ON platforms with LMEM support in case the check is wrong
>>
>> Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
>> Cc: Dave Airlie <airlied at redhat.com>
>> Cc: Daniel Vetter <daniel.vetter at intel.com>
>> ---
>>   drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 15 ++++++++++++---
>>   1 file changed, 12 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
>> index 99772f37bff60..b02dbd16bfa03 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
>> @@ -1764,7 +1764,8 @@ eb_relocate_vma_slow(struct i915_execbuffer *eb, struct eb_vma *ev)
>>          return err;
>>   }
>>
>> -static int check_relocations(const struct drm_i915_gem_exec_object2 *entry)
>> +static int check_relocations(const struct i915_execbuffer *eb,
>> +                            const struct drm_i915_gem_exec_object2 *entry)
>>   {
>>          const char __user *addr, *end;
>>          unsigned long size;
>> @@ -1774,6 +1775,14 @@ static int check_relocations(const struct drm_i915_gem_exec_object2 *entry)
>>          if (size == 0)
>>                  return 0;
>>
>> +       /* Relocations are disallowed for all platforms after TGL-LP */
>> +       if (INTEL_GEN(eb->i915) >= 12 && !IS_TIGERLAKE(eb->i915))
>> +               return -EINVAL;
>> +
>> +       /* All discrete memory platforms are Gen12 or above */
>> +       if (WARN_ON(HAS_LMEM(eb->i915)))
> 
> HAS_LMEM() will return true for the fake lmem support, which may be < gen12.
> Dropping the fake lmem would be a possibility.

Nothing in CI is currently using the fake-lmem configuration(for some 
months now I think), also its use was limited only to the selftests, 
which can't hit this path, so shouldn't matter here. Plan was to just 
drop it.

> 
> Lucas De Marchi
> 
>> +               return -EINVAL;
>> +
>>          if (size > N_RELOC(ULONG_MAX))
>>                  return -EINVAL;
>>
>> @@ -1807,7 +1816,7 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
>>                  if (nreloc == 0)
>>                          continue;
>>
>> -               err = check_relocations(&eb->exec[i]);
>> +               err = check_relocations(eb, &eb->exec[i]);
>>                  if (err)
>>                          goto err;
>>
>> @@ -1880,7 +1889,7 @@ static int eb_prefault_relocations(const struct i915_execbuffer *eb)
>>          for (i = 0; i < count; i++) {
>>                  int err;
>>
>> -               err = check_relocations(&eb->exec[i]);
>> +               err = check_relocations(eb, &eb->exec[i]);
>>                  if (err)
>>                          return err;
>>          }
>> --
>> 2.29.2
>>
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