On Mon, Dec 9, 2019 at 12:24 PM Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote: > > > > On 2019-12-09 12:23 p.m., David Hildenbrand wrote: > > 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? > > Yes, if that's what people want, it's pretty trivial to do. I chose not > to do it that way because it doesn't get passed down to add_pages() and > it's not really a "restriction". If I don't hear any objections, I will > do that for v2. +1 to storing this information alongside the altmap in that structure. However, I agree struct mhp_restrictions, with the MHP_MEMBLOCK_API flag now gone, has lost all of its "restrictions". How about dropping the 'flags' property and renaming the struct to 'struct mhp_modifiers'?
