On 09.12.19 20:13, Logan Gunthorpe wrote: > devm_memremap_pages() is currently used by the PCI P2PDMA code to create > struct page mappings for IO memory. At present, these mappings are created > with PAGE_KERNEL which implies setting the PAT bits to be WB. However, on > x86, an mtrr register will typically override this and force the cache > type to be UC-. In the case firmware doesn't set this register it is > effectively WB and will typically result in a machine check exception > when it's accessed. > > Other arches are not currently likely to function correctly seeing they > don't have any MTRR registers to fall back on. > > To solve this, add an argument to arch_add_memory() to explicitly > set the pgprot value to a specific value. > > Of the arches that support MEMORY_HOTPLUG: x86_64, s390 and arm64 is a > simple change to pass the pgprot_t down to their respective functions > which set up the page tables. For x86_32, set the page tables explicitly > using _set_memory_prot() (seeing they are already mapped). For sh, reject > anything but PAGE_KERNEL settings -- this should be fine, for now, seeing > sh doesn't support ZONE_DEVICE anyway. > > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > Cc: David Hildenbrand <david@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx> > --- > arch/arm64/mm/mmu.c | 4 ++-- > arch/ia64/mm/init.c | 5 ++++- > arch/powerpc/mm/mem.c | 4 ++-- > arch/s390/mm/init.c | 4 ++-- > arch/sh/mm/init.c | 5 ++++- > arch/x86/mm/init_32.c | 7 ++++++- > arch/x86/mm/init_64.c | 4 ++-- > include/linux/memory_hotplug.h | 2 +- > mm/memory_hotplug.c | 2 +- > mm/memremap.c | 2 +- > 10 files changed, 25 insertions(+), 14 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 60c929f3683b..48b65272df15 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1050,7 +1050,7 @@ int p4d_free_pud_page(p4d_t *p4d, unsigned long addr) > } > > #ifdef CONFIG_MEMORY_HOTPLUG > -int arch_add_memory(int nid, u64 start, u64 size, > +int arch_add_memory(int nid, u64 start, u64 size, pgprot_t prot, > struct mhp_restrictions *restrictions) Can we fiddle that into "struct mhp_restrictions" instead? -- Thanks, David / dhildenb
