Messages in this thread | | | From | Dan Williams <> | Date | Mon, 1 May 2017 09:00:04 -0700 | Subject | Re: [PATCH v2] x86/mm: Fix incorrect for loop count calculation in sync_global_pgds |
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On Mon, May 1, 2017 at 8:55 AM, Baoquan He <bhe@redhat.com> wrote: > Jeff Moyer reported that on his system with two memory regions 0~64G and > 1T~1T+192G, and kernel option "memmap=192G!1024G" added, enabling kaslr > will make system hang intermittently during boot. While adding 'nokaslr' > won't. > > This is because the for loop count calculation in sync_global_pgds is > not correct. When a mapping area crosses pgd entries, we should > calculate the starting address of region which next pgd covers and assign > it to next for loop count, but not add PGDIR_SIZE directly. The old > code works right only if the mapping area is times of PGDIR_SIZE, > otherwize the end region could be skipped so that it can't be synchronized > to all other processes from kernel pgd init_mm.pgd. > > In Jeff's system, emulated pmem area [1024G, 1216G) is smaller than > PGDIR_SIZE. While 'nokaslr' works because PAGE_OFFSET is 1T aligned, it > makes this area be mapped inside one pgd entry. With kaslr enabled, > this area could cross two pgd entries, then the next pgd entry won't > be synced to all other processes. That is why we saw empty PGD. > > Fix it in this patch. > [..] > > Reported-by: Jeff Moyer <jmoyer@redhat.com> > Signed-off-by: Baoquan He <bhe@redhat.com> [..]
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
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