Re: [PATCH] arm64: mm: Add PTE_DIRTY back to PAGE_KERNEL* to fix kexec/hibernation

["Huang, Ying" <ying.huang@linux.alibaba.com>]

Catalin Marinas <catalin.marinas@arm.com> writes:

> Commit 143937ca51cc ("arm64, mm: avoid always making PTE dirty in
> pte_mkwrite()") changed pte_mkwrite_novma() to only clear PTE_RDONLY
> when PTE_DIRTY is set. This was to allow writable-clean PTEs for swap
> pages that haven't actually been written.
>
> However, this broke kexec and hibernation for some platforms. Both go
> through trans_pgd_create_copy() -> _copy_pte(), which calls
> pte_mkwrite_novma() to make the temporary linear-map copy fully
> writable. With the updated pte_mkwrite_novma(), read-only kernel pages
> (without PTE_DIRTY) remain read-only in the temporary mapping.
> While such behaviour is fine for user pages where hardware DBM or
> trapping will make them writeable, subsequent in-kernel writes by the
> kexec relocation code will fault.
>
> Add PTE_DIRTY back to all _PAGE_KERNEL* protection definitions. This was
> the case prior to 5.4, commit aa57157be69f ("arm64: Ensure
> VM_WRITE|VM_SHARED ptes are clean by default"). With the kernel
> linear-map PTEs always having PTE_DIRTY set, pte_mkwrite_novma()
> correctly clears PTE_RDONLY.
>
> Fixes: 143937ca51cc ("arm64, mm: avoid always making PTE dirty in pte_mkwrite()")
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: <stable@vger.kernel.org>
> Reported-by: Jianpeng Chang <jianpeng.chang.cn@windriver.com>
> Link: https://lore.kernel.org/r/20251204062722.3367201-1-jianpeng.chang.cn@windriver.com
> Cc: Will Deacon <will@kernel.org>
> Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
> Cc: Guenter Roeck <linux@roeck-us.net>

LGTM, Thanks!  Feel free to add my

Reviewed-by: Huang Ying <ying.huang@linux.alibaba.com>

in the future versions.

> ---
>
> Since no-one posted this as a proper patch, here it is. However, I could
> not reproduce the initial kexec failure, so for me kexec is working with
> our without this patch.
>
> Testing appreciated before we decide to merge it. Thanks.
>
>  arch/arm64/include/asm/pgtable-prot.h | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
> index 2b32639160de..f560e6420267 100644
> --- a/arch/arm64/include/asm/pgtable-prot.h
> +++ b/arch/arm64/include/asm/pgtable-prot.h
> @@ -50,11 +50,11 @@
>  
>  #define _PAGE_DEFAULT		(_PROT_DEFAULT | PTE_ATTRINDX(MT_NORMAL))
>  
> -#define _PAGE_KERNEL		(PROT_NORMAL)
> -#define _PAGE_KERNEL_RO		((PROT_NORMAL & ~PTE_WRITE) | PTE_RDONLY)
> -#define _PAGE_KERNEL_ROX	((PROT_NORMAL & ~(PTE_WRITE | PTE_PXN)) | PTE_RDONLY)
> -#define _PAGE_KERNEL_EXEC	(PROT_NORMAL & ~PTE_PXN)
> -#define _PAGE_KERNEL_EXEC_CONT	((PROT_NORMAL & ~PTE_PXN) | PTE_CONT)
> +#define _PAGE_KERNEL		(PROT_NORMAL | PTE_DIRTY)
> +#define _PAGE_KERNEL_RO		((PROT_NORMAL & ~PTE_WRITE) | PTE_RDONLY | PTE_DIRTY)
> +#define _PAGE_KERNEL_ROX	((PROT_NORMAL & ~(PTE_WRITE | PTE_PXN)) | PTE_RDONLY | PTE_DIRTY)
> +#define _PAGE_KERNEL_EXEC	((PROT_NORMAL & ~PTE_PXN) | PTE_DIRTY)
> +#define _PAGE_KERNEL_EXEC_CONT	((PROT_NORMAL & ~PTE_PXN) | PTE_CONT | PTE_DIRTY)
>  
>  #define _PAGE_SHARED		(_PAGE_DEFAULT | PTE_USER | PTE_RDONLY | PTE_NG | PTE_PXN | PTE_UXN | PTE_WRITE)
>  #define _PAGE_SHARED_EXEC	(_PAGE_DEFAULT | PTE_USER | PTE_RDONLY | PTE_NG | PTE_PXN | PTE_WRITE)

---
Best Regards,
Huang, Ying