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

[Dan Williams]

On Fri, Feb 21, 2020 at 10:25 AM Logan Gunthorpe <logang@xxxxxxxxxxxx> 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@xxxxxxxxx>
> Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> Acked-by: David Hildenbrand <david@xxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
>  arch/arm64/mm/mmu.c            | 3 ++-
>  arch/ia64/mm/init.c            | 3 +++
>  arch/powerpc/mm/mem.c          | 3 ++-
>  arch/s390/mm/init.c            | 3 +++
>  arch/sh/mm/init.c              | 3 +++
>  arch/x86/mm/init_32.c          | 5 +++++
>  arch/x86/mm/init_64.c          | 2 +-
>  include/linux/memory_hotplug.h | 2 ++
>  mm/memory_hotplug.c            | 5 ++++-
>  mm/memremap.c                  | 6 +++---
>  10 files changed, 28 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index ee37bca8aba8..ea3fa844a8a2 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1058,7 +1058,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
>                 flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>
>         __create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start),
> -                            size, PAGE_KERNEL, __pgd_pgtable_alloc, flags);
> +                            size, params->pgprot, __pgd_pgtable_alloc,
> +                            flags);
>
>         memblock_clear_nomap(start, size);
>
> diff --git a/arch/ia64/mm/init.c b/arch/ia64/mm/init.c
> index 97bbc23ea1e3..d637b4ea3147 100644
> --- a/arch/ia64/mm/init.c
> +++ b/arch/ia64/mm/init.c
> @@ -676,6 +676,9 @@ int arch_add_memory(int nid, u64 start, u64 size,
>         unsigned long nr_pages = size >> PAGE_SHIFT;
>         int ret;
>
> +       if (WARN_ON_ONCE(params->pgprot.pgprot != PAGE_KERNEL.pgprot))
> +               return -EINVAL;
> +
>         ret = __add_pages(nid, start_pfn, nr_pages, params);
>         if (ret)
>                 printk("%s: Problem encountered in __add_pages() as ret=%d\n",
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index 19b1da5d7eca..832412bc7fad 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -138,7 +138,8 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
>         resize_hpt_for_hotplug(memblock_phys_mem_size());
>
>         start = (unsigned long)__va(start);
> -       rc = create_section_mapping(start, start + size, nid, PAGE_KERNEL);
> +       rc = create_section_mapping(start, start + size, nid,
> +                                   params->pgprot);
>         if (rc) {
>                 pr_warn("Unable to create mapping for hot added memory 0x%llx..0x%llx: %d\n",
>                         start, start + size, rc);
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index e9e4a7abd0cc..87b2d024e75a 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -277,6 +277,9 @@ int arch_add_memory(int nid, u64 start, u64 size,
>         if (WARN_ON_ONCE(params->altmap))
>                 return -EINVAL;
>
> +       if (WARN_ON_ONCE(params->pgprot.pgprot != PAGE_KERNEL.pgprot))
> +               return -EINVAL;
> +
>         rc = vmem_add_mapping(start, size);
>         if (rc)
>                 return rc;
> diff --git a/arch/sh/mm/init.c b/arch/sh/mm/init.c
> index e5114c053364..b9de2d4fa57e 100644
> --- a/arch/sh/mm/init.c
> +++ b/arch/sh/mm/init.c
> @@ -412,6 +412,9 @@ int arch_add_memory(int nid, u64 start, u64 size,
>         unsigned long nr_pages = size >> PAGE_SHIFT;
>         int ret;
>
> +       if (WARN_ON_ONCE(params->pgprot.pgprot != PAGE_KERNEL.pgprot)
> +               return -EINVAL;
> +
>         /* We only have ZONE_NORMAL, so this is easy.. */
>         ret = __add_pages(nid, start_pfn, nr_pages, params);
>         if (unlikely(ret))
> diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
> index e25a4218e6ff..96d8e4fb1cc8 100644
> --- a/arch/x86/mm/init_32.c
> +++ b/arch/x86/mm/init_32.c
> @@ -858,6 +858,11 @@ int arch_add_memory(int nid, u64 start, u64 size,
>  {
>         unsigned long start_pfn = start >> PAGE_SHIFT;
>         unsigned long nr_pages = size >> PAGE_SHIFT;
> +       int ret;
> +
> +       ret = _set_memory_prot(start, nr_pages, params->pgprot);

Perhaps a comment since it's not immediately obvious where the
PAGE_KERNEL prot was established, and perhaps add a conditional to
skip this call in the param->pgprot == PAGE_KERNEL case?

Other than that looks good to me, but only an ack since I'm only
testing the x86 changes.

Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx>