On Mon, Dec 9, 2019 at 12:47 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Mon 09-12-19 13:24:19, Logan Gunthorpe 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. > > I do agree that restriction is not the best fit. But I consider prot > argument to complicate the API to all users even though it is not really > clear whether we are going to have many users really benefiting from it. > Look at the vmalloc API and try to find how many users of __vmalloc do > not use PAGE_KERNEL. At least for this I can foresee at least one more user in the pipeline, encrypted memory support for persistent memory mappings that will store the key-id in the ptes. > > So I can see two options. One of them is to add arch_add_memory_prot > that would allow to have give and extra prot argument or simply call > an arch independent API to change the protection after arch_add_memory. > The later sounds like much less code. The memory shouldn't be in use by > anybody at that stage yet AFAIU. Maybe there even is an API like that. I'm ok with passing it the same way as altmap or a new arch_add_memory_prot() my only hangup with after the fact changes is the wasted effort it inflicts in the init path for potentially large address ranges.
