Re: [PATCH][next] drm/nouveau: svm: Avoid -Wflex-array-member-not-at-end warning

[Kees Cook]

On Wed, Apr 02, 2025 at 03:39:07PM -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition of
> a flexible structure where the size of the flexible-array member
> is known at compile-time, and refactor the rest of the code,
> accordingly.
> 
> So, with these changes, fix the following warning:
> 
> drivers/gpu/drm/nouveau/nouveau_svm.c:724:44: warning: structure containing a 
> flexible array member is not at the end of another structure 
> [-Wflex-array-member-not-at-end]
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo...@kernel.org>
> ---
>  drivers/gpu/drm/nouveau/nouveau_svm.c | 39 +++++++++++++--------------
>  1 file changed, 18 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c 
> b/drivers/gpu/drm/nouveau/nouveau_svm.c
> index e12e2596ed84..6fa387da0637 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_svm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
> @@ -720,10 +720,7 @@ nouveau_svm_fault(struct work_struct *work)
>       struct nouveau_svm *svm = container_of(buffer, typeof(*svm), 
> buffer[buffer->id]);
>       struct nvif_object *device = &svm->drm->client.device.object;
>       struct nouveau_svmm *svmm;
> -     struct {
> -             struct nouveau_pfnmap_args i;
> -             u64 phys[1];
> -     } args;
> +     DEFINE_RAW_FLEX(struct nouveau_pfnmap_args, args, p.phys, 1);
>       unsigned long hmm_flags;
>       u64 inst, start, limit;
>       int fi, fn;
> @@ -772,11 +769,11 @@ nouveau_svm_fault(struct work_struct *work)
>       mutex_unlock(&svm->mutex);
>  
>       /* Process list of faults. */
> -     args.i.i.version = 0;
> -     args.i.i.type = NVIF_IOCTL_V0_MTHD;
> -     args.i.m.version = 0;
> -     args.i.m.method = NVIF_VMM_V0_PFNMAP;
> -     args.i.p.version = 0;
> +     args->i.version = 0;
> +     args->i.type = NVIF_IOCTL_V0_MTHD;
> +     args->m.version = 0;
> +     args->m.method = NVIF_VMM_V0_PFNMAP;
> +     args->p.version = 0;
>  
>       for (fi = 0; fn = fi + 1, fi < buffer->fault_nr; fi = fn) {
>               struct svm_notifier notifier;
> @@ -802,9 +799,9 @@ nouveau_svm_fault(struct work_struct *work)
>                * fault window, determining required pages and access
>                * permissions based on pending faults.
>                */
> -             args.i.p.addr = start;
> -             args.i.p.page = PAGE_SHIFT;
> -             args.i.p.size = PAGE_SIZE;
> +             args->p.addr = start;
> +             args->p.page = PAGE_SHIFT;
> +             args->p.size = PAGE_SIZE;
>               /*
>                * Determine required permissions based on GPU fault
>                * access flags.
> @@ -832,16 +829,16 @@ nouveau_svm_fault(struct work_struct *work)
>  
>               notifier.svmm = svmm;
>               if (atomic)
> -                     ret = nouveau_atomic_range_fault(svmm, svm->drm,
> -                                                      &args.i, sizeof(args),
> +                     ret = nouveau_atomic_range_fault(svmm, svm->drm, args,
> +                                                      __struct_size(args),
>                                                        &notifier);
>               else
> -                     ret = nouveau_range_fault(svmm, svm->drm, &args.i,
> -                                               sizeof(args), hmm_flags,
> -                                               &notifier);
> +                     ret = nouveau_range_fault(svmm, svm->drm, args,
> +                                               __struct_size(args),
> +                                               hmm_flags, &notifier);
>               mmput(mm);
>  
> -             limit = args.i.p.addr + args.i.p.size;
> +             limit = args->p.addr + args->p.size;
>               for (fn = fi; ++fn < buffer->fault_nr; ) {
>                       /* It's okay to skip over duplicate addresses from the
>                        * same SVMM as faults are ordered by access type such
> @@ -855,14 +852,14 @@ nouveau_svm_fault(struct work_struct *work)
>                       if (buffer->fault[fn]->svmm != svmm ||
>                           buffer->fault[fn]->addr >= limit ||
>                           (buffer->fault[fi]->access == FAULT_ACCESS_READ &&
> -                          !(args.phys[0] & NVIF_VMM_PFNMAP_V0_V)) ||
> +                          !(args->p.phys[0] & NVIF_VMM_PFNMAP_V0_V)) ||
>                           (buffer->fault[fi]->access != FAULT_ACCESS_READ &&
>                            buffer->fault[fi]->access != FAULT_ACCESS_PREFETCH 
> &&
> -                          !(args.phys[0] & NVIF_VMM_PFNMAP_V0_W)) ||
> +                          !(args->p.phys[0] & NVIF_VMM_PFNMAP_V0_W)) ||
>                           (buffer->fault[fi]->access != FAULT_ACCESS_READ &&
>                            buffer->fault[fi]->access != FAULT_ACCESS_WRITE &&
>                            buffer->fault[fi]->access != FAULT_ACCESS_PREFETCH 
> &&
> -                          !(args.phys[0] & NVIF_VMM_PFNMAP_V0_A)))
> +                          !(args->p.phys[0] & NVIF_VMM_PFNMAP_V0_A)))
>                               break;
>               }
>  

LGTM, including the __struct_size() usage.

Reviewed-by: Kees Cook <k...@kernel.org>

-- 
Kees Cook