linux-kernel - Re: [PATCH v2 2/2] kexec: Provide arch_kexec_protect(unprotect)

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Date:	Thu, 7 Jan 2016 01:08:32 +0800
From:	Minfei Huang <mhuang@...hat.com>
To:	Xunlei Pang <xlpang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	akpm@...ux-foundation.org, ebiederm@...ssion.com,
	Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH v2 2/2] kexec: Provide
 arch_kexec_protect(unprotect)_crashkres()

On 01/06/16 at 05:50pm, Xunlei Pang wrote:
> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> index 819ab3f..cda867d 100644
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -536,3 +536,44 @@ overflow:
>  	return -ENOEXEC;
>  }
>  #endif /* CONFIG_KEXEC_FILE */
> +
> +static int
> +kexec_mark_range(unsigned long start, unsigned long end, bool protect)
> +{
> +	struct page *page;
> +	unsigned int nr_pages;
> +
> +	/* For physical range: [start, end] */
> +	if (!start || !end || start > end)
> +		return 0;

Hi, Xunlei.

        if (start > end)
                return 0;

See the below comment.
> +
> +	page = pfn_to_page(start >> PAGE_SHIFT);
> +	nr_pages = (end + PAGE_SIZE - start) >> PAGE_SHIFT;

As I commented in last version, it is better to cover the case if the
range from start to end acrosses two pages.

> +	if (protect)
> +		return set_pages_ro(page, nr_pages);
> +	else
> +		return set_pages_rw(page, nr_pages);
> +}
> +
> +static void kexec_mark_crashkres(bool protect)
> +{
> +	unsigned long control;
> +
> +	kexec_mark_range(crashk_low_res.start, crashk_low_res.end, protect);

Adding the following if test to test crashk_low_res is better. Then we
do not need to test if start or end is equal to 0 in kexec_mark_range.

        if (crashk_low_res.start != crashk_low_res.end) {
                kexec_mark_range(crashk_low_res.start,
                                crashk_low_res.end, protect);
        }

> +
> +	/* Don't touch the control code page used in crash_kexec().*/
> +	control = PFN_PHYS(page_to_pfn(kexec_crash_image->control_code_page));
> +	/* Control code page is located in the 2nd page. */
> +	kexec_mark_range(crashk_res.start, control + PAGE_SIZE - 1, protect);
> +	kexec_mark_range(control + 2 * PAGE_SIZE, crashk_res.end, protect);

I think it is more readable, if we use MACRO KEXEC_CONTROL_PAGE_SIZE,
instead of using 2*PAGE_SIZE directly.

Thanks
Minfei
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