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

[Zbigniew Kempczyński]

On Wed, Mar 10, 2021 at 03:50:07PM -0600, Jason Ekstrand 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

I was asked to review of this patch. It works along with expected
IGT check https://patchwork.freedesktop.org/patch/423361/?series=82954&rev=25

Before I'll give you r-b - isn't i915_gem_execbuffer2_ioctl() better place
to do for loop just after copy_from_user() and check relocation_count?
We have an access to exec2_list there, we know the gen so we're able to say
relocations are not supported immediate, without entering i915_gem_do_execbuffer().

--
Zbigniew

> 
> 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)))
> +		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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