Re: [RFC v2 4/5] x86/crash: make the page that stores the LUKS volume key inaccessible

[Coiby Xu]

Hi Dave,

Thanks for the quick review!

On Fri, Nov 04, 2022 at 07:38:17AM -0700, Dave Hansen wrote:
> On 11/4/22 04:29, Coiby Xu wrote:
> > +	if (kexec_crash_image->luks_volume_key_addr) {
> > +		start = kexec_crash_image->luks_volume_key_addr;
> > +		end = start + kexec_crash_image->luks_volume_key_sz - 1;
> > +		page = pfn_to_page(start >> PAGE_SHIFT);
> > +		nr_pages = (end >> PAGE_SHIFT) - (start >> PAGE_SHIFT) + 1;
> > +		set_memory_np((unsigned long)page_address(page), nr_pages);
> > +	}
>
> Why does this go pfn -> page -> vaddr?  What good does having the page
> do? 

Sorry it's an imitation of kexec_mark_crashkres.

> Can you just do phys_to_virt() on the start address?  Maybe:
>
> 	start_paddr = kexec_crash_image->luks_volume_key_addr;
> 	end_paddr   = start_paddr + kexec_crash_image->luks_volume_key_sz - 1;
> 	nr_pages = (PAGE_ALIGN(end_paddr) - PAGE_ALIGN_DOWN(start_paddr))/
> PAGE_SIZE;
> 	set_memory_np((unsigned long)phys_to_virt(start_paddr), nr_pages);

Thanks for suggesting a smarter implementation! I'll apply it to next
version.

> Also, if you resend this, please just cc the x86 folks on the series.
> The other patches and cover letter have desperately needed context
> around this.

Sure, I'll cc the x86 list the complete patch set next time. Sorry
you'll have to go to
https://lore.kernel.org/lkml/20221104113000.487098-5-coxu@xxxxxxxxxx/t/
to read related emails for now.


>

--
Best regards,
Coiby