Date: Sat, 26 Dec 2015 23:21:00 +0800
From: Minfei Huang <mhuang@redhat.com>
To: Xunlei Pang <xlpang@redhat.com>
Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
        akpm@linux-foundation.org, Eric Biederman <ebiederm@xmission.com>
Subject: Re: [PATCH 2/2] kexec: Provide
 arch_kexec_protect(unprotect)_crashkres()
Message-ID: <20151226152100.GA26946@dhcp-128-25.nay.redhat.com>
References: <1450869146-6186-1-git-send-email-xlpang@redhat.com>
 <1450869146-6186-2-git-send-email-xlpang@redhat.com>
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On 12/23/15 at 07:12pm, Xunlei Pang wrote:
> Implement the protection method for the crash kernel memory
> reservation for the 64-bit x86 kdump.
> 
> Signed-off-by: Xunlei Pang <xlpang@redhat.com>
> ---
> Only provided x86_64 implementation, as I've only tested on x86_64 so far.
> 
>  arch/x86/kernel/machine_kexec_64.c | 43 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 43 insertions(+)
> 
> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> index 819ab3f..a3d289c 100644
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -536,3 +536,46 @@ overflow:
>  	return -ENOEXEC;
>  }
>  #endif /* CONFIG_KEXEC_FILE */
> +
> +#ifdef CONFIG_KEXEC_CORE
> +static int
> +kexec_mark_range(unsigned long start, unsigned long end, bool protect)
> +{
> +	struct page *page;
> +	unsigned int nr_pages;
> +
> +	if (!start || !end || start >= end)
> +		return 0;
> +
> +	page = pfn_to_page(start >> PAGE_SHIFT);
> +	nr_pages = (end + 1 - start) >> PAGE_SHIFT;

The start and end may across two pages, although the range is small than
PAGE_SIZE. You can use following to calculate count of page.

nr_pages = (end >> PAGE_SHIFT) - (start >> PAGE_SHIFT) + 1;

Thanks
Minfei

> +	if (protect)
> +		return set_pages_ro(page, nr_pages);
> +	else
> +		return set_pages_rw(page, nr_pages);
> +}
--
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