Re: [bug report] mm: replace vma->vm_flags direct modifications with modifier calls

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Wed, Jul 12, 2023 at 07:49:53PM +0100, Matthew Wilcox wrote:
> @@ -964,9 +966,12 @@ vm_fault_t gru_fault(struct vm_fault *vmf)
>  		}
>  		gru_load_context(gts);
>  		paddr = gseg_physical_address(gts->ts_gru, gts->ts_ctxnum);
> -		remap_pfn_range(vma, vaddr & ~(GRU_GSEG_PAGESIZE - 1),
> -				paddr >> PAGE_SHIFT, GRU_GSEG_PAGESIZE,
> -				vma->vm_page_prot);
> +
> +		pte = pfn_pte(paddr / PAGE_SIZE, vma->vm_page_prot);
> +		ptep = vmf->pte - (vaddr % GRU_GSEG_PAGESIZE) / PAGE_SIZE;
> +		set_ptes(vma->vm_mm, vaddr & ~(GRU_GSEG_PAGESIZE - 1),
> +				ptep, pte_mkspecial(pte),
> +				GRU_GSEG_PAGESIZE / PAGE_SIZE);
>  	}

Argh, no, this is wrong.  The page table isn't mapped at this point.
What we want is a cross between vmf_insert_pfn() and vm_insert_pages().
Let me add that ...