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Date: Thu, 7 Jan 2016 10:20:31 +0800
From: Xunlei Pang <xlpang@...hat.com>
To: Minfei Huang <mhuang@...hat.com>
Cc: kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
ebiederm@...ssion.com, akpm@...ux-foundation.org,
Dave Young <dyoung@...hat.com>, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH v2 2/2] kexec: Provide
arch_kexec_protect(unprotect)_crashkres()
On 01/07/2016 at 10:14 AM, Xunlei Pang wrote:
> 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;
In fact, control code page is only 1 page, using control + 2*PAGE_SIZE is clearer.
For example, if we have more other type pages following it. Anyway this is not
that important.
Regards,
Xunlei
> + 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
>>
>> _______________________________________________
>> kexec mailing list
>> kexec@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/kexec
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