Let's CC Hpa on this one. I am still not sure it is correct. The full series is here http://lkml.kernel.org/r/1502138329-123460-1-git-send-email-pasha.tatashin@xxxxxxxxxx On Mon 07-08-17 16:38:35, Pavel Tatashin wrote: > Struct pages are initialized by going through __init_single_page(). Since > the existing physical memory in memblock is represented in memblock.memory > list, struct page for every page from this list goes through > __init_single_page(). > > The second memblock list: memblock.reserved, manages the allocated memory. > The memory that won't be available to kernel allocator. So, every page from > this list goes through reserve_bootmem_region(), where certain struct page > fields are set, the assumption being that the struct pages have been > initialized beforehand. > > In trim_low_memory_range() we unconditionally reserve memoryfrom PFN 0, but > memblock.memory might start at a later PFN. For example, in QEMU, > e820__memblock_setup() can use PFN 1 as the first PFN in memblock.memory, > so PFN 0 is not on memblock.memory (and hence isn't initialized via > __init_single_page) but is on memblock.reserved (and hence we set fields in > the uninitialized struct page). > > Currently, the struct page memory is always zeroed during allocation, > which prevents this problem from being detected. But, if some asserts > provided by CONFIG_DEBUG_VM_PGFLAGS are tighten, this problem may become > visible in existing kernels. > > In this patchset we will stop zeroing struct page memory during allocation. > Therefore, this bug must be fixed in order to avoid random assert failures > caused by CONFIG_DEBUG_VM_PGFLAGS triggers. > > The fix is to reserve memory from the first existing PFN. > > Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> > Reviewed-by: Steven Sistare <steven.sistare@xxxxxxxxxx> > Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> > Reviewed-by: Bob Picco <bob.picco@xxxxxxxxxx> > --- > arch/x86/kernel/setup.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > index 3486d0498800..489cdc141bcb 100644 > --- a/arch/x86/kernel/setup.c > +++ b/arch/x86/kernel/setup.c > @@ -790,7 +790,10 @@ early_param("reservelow", parse_reservelow); > > static void __init trim_low_memory_range(void) > { > - memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE)); > + unsigned long min_pfn = find_min_pfn_with_active_regions(); > + phys_addr_t base = min_pfn << PAGE_SHIFT; > + > + memblock_reserve(base, ALIGN(reserve_low, PAGE_SIZE)); > } > > /* > -- > 2.14.0 -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
