Re: [PATCH 2/2] riscv: mm: check the valid bit in kernel_page_present()

[Jisheng Zhang <jszhang@kernel.org>]

On Thu, Nov 12, 2026 at 03:42:19PM +0200, Mike Rapoport (Microsoft) wrote:
> set_direct_map_invalid_noflush() clears _PAGE_PRESENT, but the kernel
> mappings keep _PAGE_PROT_NONE set: it used to be _PAGE_READ and now it is
> the same bit as _PAGE_GLOBAL. pte_present() and pmd_present() still
> return true for the invalidated entry. kernel_page_present() then reports
> that an unmapped page is mapped, and hibernation copies it without
> remapping it first.
> 
> Test _PAGE_PRESENT directly for PMD and PTE leaves.
> 
> Fixes: 32a0de886eb3 ("arch, mm: make kernel_page_present() always available")
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>  arch/riscv/mm/pageattr.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
> index b138113755359..62fbcf7cf36b6 100644
> --- a/arch/riscv/mm/pageattr.c
> +++ b/arch/riscv/mm/pageattr.c
> @@ -453,8 +453,9 @@ bool kernel_page_present(struct page *page)
>  	if (!pmd_present(pmdp_get(pmd)))
>  		return false;
>  	if (pmd_leaf(pmdp_get(pmd)))
> -		return true;
> +		return pmd_val(pmdp_get(pmd)) & _PAGE_PRESENT;

so we call pmdp_get() up to 3 times, could we save its result
and reuse it?

>  
> +	/* pte_present() is true for PAGE_KERNEL with _PAGE_PRESENT cleared */
>  	pte = pte_offset_kernel(pmd, addr);
> -	return pte_present(ptep_get(pte));
> +	return pte_val(ptep_get(pte)) & _PAGE_PRESENT;
>  }
> 
> -- 
> 2.53.0
> 
> 
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