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

[Xunlei Pang <xlpang@redhat.com>]

On 12/24/2015 at 02:16 PM, Dave Young wrote:
> Hi, Xunlei
>
> On 12/24/15 at 02:05pm, Xunlei Pang wrote:
>> 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.
> Ok, I have no strong opinion on that..
>
>>>> +}
>>>> +
>>>> +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;
> Though it works because the control code is less than 1 page, but use the macro
> of KEXEC_CONTROL_PAGE_SIZE looks better..
>
>>>> +	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.
> Ok, that's fine.

At least moving the x86 control-copying code into arch-related
machine_kexec_prepare() should work, and this can omit the
special treatment of the control code page.

Regards,
Xunlei

>
>> 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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> Thanks
> Dave
>
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