Re: [PATCH v3 6/7] mm/memory_hotplug: Add pgprot_t to mhp_params

David Hildenbrand
2020-02-24T09:26:24Z

On 21.02.20 19:25, 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, provide a way to specify the pgprot value explicitly to
> arch_add_memory().
>
> Of the arches that support MEMORY_HOTPLUG: x86_64, and arm64 need 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 ia64, s390 and
> sh, reject anything but PAGE_KERNEL settings -- this should be fine,
> for now, seeing these architectures don't support ZONE_DEVICE.
>
> A check in __add_pages() is also added to ensure the pgprot parameter was
> set for all arches.
>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

[...]

> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index c5df1b3dada0..30d6c1b8847e 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -56,9 +56,11 @@ enum {
> /*
> * Extended parameters for memory hotplug:
> * altmap: alternative allocator for memmap array (optional)
> + * pgprot: page protection flags to apply to newly added page tables (required)

s/added/created/?

--
Thanks,

David / dhildenb