linux-kernel - Re: [PATCH v3 6/7] mm/memory_hotplug: Add pgprot_t to mhp

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Date:   Mon, 24 Feb 2020 10:26:10 +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,
        Dan Williams <dan.j.williams@...el.com>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Christoph Hellwig <hch@....de>,
        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>,
        Eric Badger <ebadger@...aio.com>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v3 6/7] mm/memory_hotplug: Add pgprot_t to mhp_params

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