On Wed, Feb 28, 2018 at 08:33:59PM +0800, Dave Young wrote: > On 02/26/18 at 07:24pm, AKASHI Takahiro wrote: > > On Fri, Feb 23, 2018 at 04:49:34PM +0800, Dave Young wrote: > > > Hi AKASHI, > > > > > > On 02/22/18 at 08:17pm, AKASHI Takahiro wrote: > > > > On arm64, no trampline code between old kernel and new kernel will be > > > > required in kexec_file implementation. This patch introduces a new > > > > configuration, ARCH_HAS_KEXEC_PURGATORY, and allows related code to be > > > > compiled in only if necessary. > > > > > > Here also need the explanation about why no purgatory is needed, it would be > > > required for kexec if no strong reason. > > > > OK, I will add the reason: > > On arm64, crash dump kernel's usable memory is protected by > > *unmapping* it from kernel virtual space unlike other architectures > > where the region is just made read-only. > > So our key developers think that it is highly unlikely that the region > > is accidentally corrupted and this rationalizes that digest check code > > be also dropped from purgatory. > > This greatly simplifies our purgatory without any need for a bit ugly > > relocation stuff, i.e. arch_kexec_apply_relocations_add(). > > > > Please see: > > http://lists.infradead.org/pipermail/linux-arm-kernel/2017-December/545428.html > > to find out how simple our purgatory was. All that it does is > > to shuffle arguments and jump into a new kernel. > > > > Without this patch, we would have to have purgatory with a space for > > a hash value (purgatory_sha256_digest) which is never checked against. > > > > Do you think it makes sense? > > Hmm, it looks reasonable, I remember there could be some performance > issue for a purgatory because of cache disabled for arm64. I do not > object this. Yeah, Pratyush(redhat) had expressed his concerns on slow boot-up of the 2nd kernel which is due to hash value calculation. -Takahiro AKASHI > > [snip] > > Thanks > Dave _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
