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

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Message-ID: <20151224055425.GC3480@dhcp-128-65.nay.redhat.com>
Date:	Thu, 24 Dec 2015 13:54:25 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Xunlei Pang <xlpang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	akpm@...ux-foundation.org, Eric Biederman <ebiederm@...ssion.com>,
	vgoyal@...hat.com
Subject: Re: [PATCH 2/2] kexec: Provide
 arch_kexec_protect(unprotect)_crashkres()

Ccing Vivek

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@...hat.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

The file is only compiled when CONFIG_KEXEC_CORE=y so #ifdef is not necessary

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

May use set_memory_ro/rw to avoid converting to *page?

> +}
> +
> +static void kexec_mark_crashkres(bool protect)
> +{
> +	unsigned long control;
> +
> +	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. */
> +	control = control + PAGE_SIZE;
> +	kexec_mark_range(crashk_res.start, control - 1, protect);
> +	kexec_mark_range(control + PAGE_SIZE, crashk_res.end, protect);

X86 kexec will copy the page while kexecing, could you check if we can move
that copying to earliyer while kexec loading, maybe machine_kexec_prepare so
that we can make a arch-independent implementation.

> +}
> +
> +void arch_kexec_protect_crashkres(void)
> +{
> +	kexec_mark_crashkres(true);
> +}
> +
> +void arch_kexec_unprotect_crashkres(void)
> +{
> +	kexec_mark_crashkres(false);
> +}
> +#endif
> -- 
> 2.5.0
> 
> 
> _______________________________________________
> kexec mailing list
> kexec@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
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