Re: [PATCH v2 2/2] kexec: Provide arch_kexec_protect(unprotect)_crashkres()

[Xunlei Pang <xlpang@redhat.com>]

On 01/07/2016 at 01:08 AM, Minfei Huang wrote:
> On 01/06/16 at 05:50pm, Xunlei Pang wrote:
>> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
>> index 819ab3f..cda867d 100644
>> --- a/arch/x86/kernel/machine_kexec_64.c
>> +++ b/arch/x86/kernel/machine_kexec_64.c
>> @@ -536,3 +536,44 @@ overflow:
>>  	return -ENOEXEC;
>>  }
>>  #endif /* CONFIG_KEXEC_FILE */
>> +
>> +static int
>> +kexec_mark_range(unsigned long start, unsigned long end, bool protect)
>> +{
>> +	struct page *page;
>> +	unsigned int nr_pages;
>> +
>> +	/* For physical range: [start, end] */
>> +	if (!start || !end || start > end)
>> +		return 0;
> Hi, Xunlei.
>
>         if (start > end)
>                 return 0;

If both start and end are zero, we want to return directly, so the two
more check doesn't hurt.

> See the below comment.
>> +
>> +	page = pfn_to_page(start >> PAGE_SHIFT);
>> +	nr_pages = (end + PAGE_SIZE - start) >> PAGE_SHIFT;
> As I commented in last version, it is better to cover the case if the
> range from start to end acrosses two pages.

right.

>> +	if (protect)
>> +		return set_pages_ro(page, nr_pages);
>> +	else
>> +		return set_pages_rw(page, nr_pages);
>> +}
>> +
>> +static void kexec_mark_crashkres(bool protect)
>> +{
>> +	unsigned long control;
>> +
>> +	kexec_mark_range(crashk_low_res.start, crashk_low_res.end, protect);
> Adding the following if test to test crashk_low_res is better. Then we
> do not need to test if start or end is equal to 0 in kexec_mark_range.
>
>         if (crashk_low_res.start != crashk_low_res.end) {
>                 kexec_mark_range(crashk_low_res.start,
>                                 crashk_low_res.end, protect);
>         }

The checks in kexec_mark_range() will handle the case, it's not
performance-critical path and will make the code less clean.

>> +
>> +	/* 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. */
>> +	kexec_mark_range(crashk_res.start, control + PAGE_SIZE - 1, protect);
>> +	kexec_mark_range(control + 2 * PAGE_SIZE, crashk_res.end, protect);
> I think it is more readable, if we use MACRO KEXEC_CONTROL_PAGE_SIZE,
> instead of using 2*PAGE_SIZE directly.

OK.

How about the following update:

+static int
+kexec_mark_range(unsigned long start, unsigned long end, bool protect)
+{
+       struct page *page;
+       unsigned int nr_pages;
+
+       /* For physical range: [start, end] */
+       if (!start || !end || start > end)
+               return 0;
+
+       page = pfn_to_page(start >> PAGE_SHIFT);
+       nr_pages = (end >> PAGE_SHIFT) - (start >> PAGE_SHIFT) + 1;
+       if (protect)
+               return set_pages_ro(page, nr_pages);
+       else
+               return set_pages_rw(page, nr_pages);
+}
+
+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. */
+       kexec_mark_range(crashk_res.start, control + PAGE_SIZE - 1, protect);
+       control += KEXEC_CONTROL_PAGE_SIZE;
+       kexec_mark_range(control, crashk_res.end, protect);
+}
+
+void arch_kexec_protect_crashkres(void)
+{
+       kexec_mark_crashkres(true);
+}
+
+void arch_kexec_unprotect_crashkres(void)
+{
+       kexec_mark_crashkres(false);
+}

> Thanks
> Minfei
>
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