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

[Dave Young]

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@xxxxxxxxxx>
> >> ---
> >> 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.

> 
> 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
> >>
> >>
> >> _______________________________________________
> >> kexec mailing list
> >> kexec@xxxxxxxxxxxxxxxxxxx
> >> http://lists.infradead.org/mailman/listinfo/kexec
> 
> 
> _______________________________________________
> kexec mailing list
> kexec@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/kexec

Thanks
Dave
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