Re: [PATCH RFC 09/11] misc/sgi-gru: use ptep_get() for page-table reads

On Mon, Jul 27, 2026 at 05:47:00PM +0100, Muhammad Usama Anjum wrote:
> A leaf PMD is being read through ptep_get() by treating the PMD address
> as PTE-sized table storage. ptep_get() now accepts hw_pte_t *, so update
> the cast accordingly.
> 
> pte_offset_kernel() also returns hw_pte_t *. Get pte_t value by calling
> ptep_get().
> 
> Signed-off-by: Muhammad Usama Anjum <[email protected]>
> ---
>  drivers/misc/sgi-gru/grufault.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/sgi-gru/grufault.c b/drivers/misc/sgi-gru/grufault.c
> index 3557d78ee47a2..ff89d34ad2aa4 100644
> --- a/drivers/misc/sgi-gru/grufault.c
> +++ b/drivers/misc/sgi-gru/grufault.c
> @@ -228,10 +228,10 @@ static int atomic_pte_lookup(struct vm_area_struct *vma, unsigned long vaddr,
>  		goto err;
>  #ifdef CONFIG_X86_64
>  	if (unlikely(pmd_leaf(*pmdp)))
> -		pte = ptep_get((pte_t *)pmdp);
> +		pte = ptep_get((hw_pte_t *)pmdp);
>  	else
>  #endif
> -		pte = *pte_offset_kernel(pmdp, vaddr);
> +		pte = ptep_get(pte_offset_kernel(pmdp, vaddr));
>  
>  	if (unlikely(!pte_present(pte) ||
>  		     (write && (!pte_write(pte) || !pte_dirty(pte)))))

This code is super, super broken. Can we remove this ASAP? For starters,
we're using is_vm_hugetlb_page() to detect page shift, the code does not
grab refs on the pages, uses pte_offset_kernel() on user page tables,
does not handle PUD-level hugepages, does not handle PMD-level hugepages on !x86_64,
does not hold page table locks nor check for pte table retraction, etc

I don't think I need to go on.

-- 
Pedro