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

[Xunlei Pang <xlpang@redhat.com>]

On 12/24/2015 at 02:44 PM, Xunlei Pang wrote:
> 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..

The 1st page is pagetable, control code page locates at the 2nd page.
The following kexec_mark_range() wants to mark ro from crashk_res.start
to the 1st page(included), so here we must use 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.
>> 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.

The "relocate_kernel" routine in "relocate_kernel_64.S" will use it as
a temp storage "for jumping back"(as its comment), so we can't mark
it readonly.

>
> 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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