On Thu, 28 Jan 2016 19:56:56 +0800 Xunlei Pang <xpang at redhat.com> wrote: > On 2016/01/28 at 18:32, Michael Holzheu wrote: > > On Wed, 27 Jan 2016 11:15:46 -0800 > > Andrew Morton <akpm at linux-foundation.org> wrote: > > > >> On Wed, 27 Jan 2016 14:48:31 +0300 Dmitry Safonov <dsafonov at virtuozzo.com> wrote: > >> > >>> For allocation of kimage failure or kexec_prepare or load segments > >>> errors there is no need to keep crashkernel memory mapped. > >>> It will affect only s390 as map/unmap hook defined only for it. > >>> As on unmap s390 also changes os_info structure let's check return code > >>> and add info only on success. > >>> > >> This conflicts (both mechanically and somewhat conceptually) with > >> Xunlei Pang's "kexec: Introduce a protection mechanism for the > >> crashkernel reserved memory" and "kexec: provide > >> arch_kexec_protect(unprotect)_crashkres()". > >> > >> http://ozlabs.org/~akpm/mmots/broken-out/kexec-introduce-a-protection-mechanism-for-the-crashkernel-reserved-memory.patch > >> http://ozlabs.org/~akpm/mmots/broken-out/kexec-introduce-a-protection-mechanism-for-the-crashkernel-reserved-memory-v4.patch > >> > >> and > >> > >> http://ozlabs.org/~akpm/mmots/broken-out/kexec-provide-arch_kexec_protectunprotect_crashkres.patch > >> http://ozlabs.org/~akpm/mmots/broken-out/kexec-provide-arch_kexec_protectunprotect_crashkres-v4.patch > > Hmm, It looks to me that arch_kexec_(un)protect_crashkres() has exactly > > the same semantics as crash_(un)map_reserved_pages(). > > > > On s390 we don't have the crashkernel memory mapped and therefore need > > crash_map_reserved_pages() before loading something into crashkernel > > memory. > > I don't know s390, just curious, if s390 doesn't have crash kernel memory mapped, > what's the purpose of the commit(558df7209e) for s390 as the reserved crash memory > with no kernel mapping already means the protection is on? When we reserve crashkernel memory on s390 ("crashkernel=" kernel parameter), we create a memory hole without page tables. Commit (558df7209e) was necessary to load a kernel/ramdisk into the memory hole with the kexec() system call. We create a temporary mapping with crash_map_reserved_pages(), then copy the kernel/ramdisk and finally remove the mapping again via crash_unmap_reserved_pages(). We did that all in order to protect the preloaded kernel and ramdisk. I forgot the details why commit(558df7209e) wasn't necessary before. AFAIK it became necessary because of some kdump (mmap?) rework. Michael
