On Wednesday 14 December 2016 05:07 PM, Mark Rutland wrote: > On Wed, Dec 14, 2016 at 11:16:17AM +0000, James Morse wrote: >> Hi Pratyush, >> >> On 14/12/16 10:12, Pratyush Anand wrote: >>> On Wednesday 14 December 2016 03:08 PM, Pratyush Anand wrote: >>>>> I would go as far as to generate the page tables at 'kexec -l' time, >>>>> and only if >>>> >>>> Ok..So you mean that I create a new section which will have page table >>>> entries mapping physicalmemory represented by remaining section, and >>>> then purgatory can just enable mmu with page table from that section, >>>> right? Seems doable. can do that. >>> >>> I see a problem here. If we create page table as a new segment then, how can we >>> verify in purgatory that sha for page table is correct? We need page table >>> before sha verification start,and we can not rely the page table created by >>> first kernel until it's sha is verified. So a chicken-egg problem. >> >> There is more than one of those! What happens if your sha256 calculation code is >> corrupted? You have to run it before you know. The same goes for all the >> purgatory code. >> >> This is why I think its better to do this in the kernel before we exit to >> purgatory, but obviously that doesn't work for kdump. > > I see in an earlier message that the need for sha256 was being discussed > in another thread. Do either of you happen to have a pointer to that. > patch 0/2 of this series. > To me, it seems like it doesn't come with much benefit for the kdump > case given that's best-effort anyway, and as above the verification code > could have been be corrupted. In the non-kdump case it's not strictly > necessary and seems like a debugging aid rather than a necessary piece > of functionality -- if that's the case, a 20 second delay isn't the end > of the world... Even for the non-kdump ie `kexec -l` case we do not have a functionality to bypass sha verification in kexec-tools. --lite option with the kexec-tools was discouraged and not accepted. So,it is 20s for both `kexec -l` and `kexec -p`. Also other arch like x86_64 takes negligible time in sha verification. ~Pratyush
