Subject: Re: [PATCH v12 4/6] arm64: support copy_mc_[user]_highpage()

From: Jonathan Cameron <[email-masked]>
Date: Mon, 19 Aug 2024 12:56:01 +0100

On Tue, 28 May 2024 16:59:13 +0800
Tong Tiangen <[email-masked]> wrote:

> Currently, many scenarios that can tolerate memory errors when copying page
> have been supported in the kernel[1~5], all of which are implemented by
> copy_mc_[user]_highpage(). arm64 should also support this mechanism.
> 
> Due to mte, arm64 needs to have its own copy_mc_[user]_highpage()
> architecture implementation, macros __HAVE_ARCH_COPY_MC_HIGHPAGE and
> __HAVE_ARCH_COPY_MC_USER_HIGHPAGE have been added to control it.
> 
> Add new helper copy_mc_page() which provide a page copy implementation with
> hardware memory error safe. The code logic of copy_mc_page() is the same as
> copy_page(), the main difference is that the ldp insn of copy_mc_page()
> contains the fixup type EX_TYPE_KACCESS_ERR_ZERO_ME_SAFE, therefore, the
> main logic is extracted to copy_page_template.S.
> 
> [1] commit d302c2398ba2 ("mm, hwpoison: when copy-on-write hits poison, take page offline")
> [2] commit 1cb9dc4b475c ("mm: hwpoison: support recovery from HugePage copy-on-write faults")
> [3] commit 6b970599e807 ("mm: hwpoison: support recovery from ksm_might_need_to_copy()")
> [4] commit 98c76c9f1ef7 ("mm/khugepaged: recover from poisoned anonymous memory")
> [5] commit 12904d953364 ("mm/khugepaged: recover from poisoned file-backed memory")
> 
> Signed-off-by: Tong Tiangen <[email-masked]>
Trivial stuff inline.

Jonathan

> diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
> index 5018ac03b6bf..50ef24318281 100644
> --- a/arch/arm64/lib/mte.S
> +++ b/arch/arm64/lib/mte.S
> @@ -80,6 +80,35 @@ SYM_FUNC_START(mte_copy_page_tags)
>  	ret
>  SYM_FUNC_END(mte_copy_page_tags)
>  
> +#ifdef CONFIG_ARCH_HAS_COPY_MC
> +/*
> + * Copy the tags from the source page to the destination one wiht machine check safe
Spell check.
with

Also, maybe reword given machine check doesn't make sense on arm64.

> + *   x0 - address of the destination page
> + *   x1 - address of the source page
> + * Returns:
> + *   x0 - Return 0 if copy success, or
> + *        -EFAULT if anything goes wrong while copying.
> + */
> +SYM_FUNC_START(mte_copy_mc_page_tags)
> +	mov	x2, x0
> +	mov	x3, x1
> +	multitag_transfer_size x5, x6
> +1:
> +KERNEL_ME_SAFE(2f, ldgm	x4, [x3])
> +	stgm	x4, [x2]
> +	add	x2, x2, x5
> +	add	x3, x3, x5
> +	tst	x2, #(PAGE_SIZE - 1)
> +	b.ne	1b
> +
> +	mov x0, #0
> +	ret
> +
> +2:	mov x0, #-EFAULT
> +	ret
> +SYM_FUNC_END(mte_copy_mc_page_tags)
> +#endif
> +
>  /*
>   * Read tags from a user buffer (one tag per byte) and set the corresponding
>   * tags at the given kernel address. Used by PTRACE_POKEMTETAGS.
> diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c
> index a7bb20055ce0..ff0d9ceea2a4 100644
> --- a/arch/arm64/mm/copypage.c
> +++ b/arch/arm64/mm/copypage.c
> @@ -40,3 +40,48 @@ void copy_user_highpage(struct page *to, struct page *from,

> +
> +int copy_mc_user_highpage(struct page *to, struct page *from,
> +			unsigned long vaddr, struct vm_area_struct *vma)
> +{
> +	int ret;
> +
> +	ret = copy_mc_highpage(to, from);
> +	if (!ret)
> +		flush_dcache_page(to);
Personally I'd always keep the error out of line as it tends to be
more readable when reviewing a lot of code.
	if (ret)
		return ret;

	flush_dcache_page(to);

	return 0;
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(copy_mc_user_highpage);
> +#endif