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

[Xunlei Pang <xlpang@redhat.com>]

On 12/24/2015 at 01:54 PM, Dave Young wrote:
> 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@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
> The file is only compiled when CONFIG_KEXEC_CORE=y so #ifdef is not necessary

Yes, indeed. I'll remove this macro and send v2 later.

>
>> +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?

on x86 it just a wrapper of set_memory_ro/rw, I think both are ok.

>
>> +}
>> +
>> +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.

For some arch, may use huge tlb directly to do the kernel mapping,
in such cases, we can't implement this function. So I think it should
be arch-dependent.

Regards,
Xunlei

>
>> +}
>> +
>> +void arch_kexec_protect_crashkres(void)
>> +{
>> +	kexec_mark_crashkres(true);
>> +}
>> +
>> +void arch_kexec_unprotect_crashkres(void)
>> +{
>> +	kexec_mark_crashkres(false);
>> +}
>> +#endif
>> -- 
>> 2.5.0
>>
>>
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