linux-kernel - Re: [PATCH 5/6] mm, memory_hotplug: Provide argument for the pgprot_t in arch_add

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Message-ID: <ce50d9da-c60e-05a1-a86b-3bb3629de502@redhat.com>
Date:   Mon, 9 Dec 2019 20:23:33 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, linux-mm@...ck.org,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 5/6] mm, memory_hotplug: Provide argument for the pgprot_t
 in arch_add_memory()

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@...el.com>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> ---
>  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