From: Dan Williams <dan.j.williams@intel.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Logan Gunthorpe <logang@deltatee.com>,
David Hildenbrand <david@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
linux-ia64@vger.kernel.org,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
linux-s390 <linux-s390@vger.kernel.org>,
Linux-sh <linux-sh@vger.kernel.org>,
platform-driver-x86@vger.kernel.org,
Linux MM <linux-mm@kvack.org>, Christoph Hellwig <hch@lst.de>,
Andrew Morton <akpm@linux-foundation.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 5/6] mm, memory_hotplug: Provide argument for the pgprot_t in arch_add_memory()
Date: Mon, 9 Dec 2019 13:00:13 -0800 [thread overview]
Message-ID: <CAPcyv4iKKw8cuFyDrY2VLN2ecd-qAbDCfYa7SufuhUb59e89Rw@mail.gmail.com> (raw)
In-Reply-To: <20191209204128.GC7658@dhcp22.suse.cz>
On Mon, Dec 9, 2019 at 12:47 PM Michal Hocko <mhocko@kernel.org> 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@intel.com>
> > >> Cc: David Hildenbrand <david@redhat.com>
> > >> Cc: Michal Hocko <mhocko@suse.com>
> > >> Signed-off-by: Logan Gunthorpe <logang@deltatee.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?
> >
> > 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.
next prev parent reply other threads:[~2019-12-09 21:00 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-09 19:13 [PATCH 0/6] Allow setting caching mode in arch_add_memory() for P2PDMA Logan Gunthorpe
2019-12-09 19:13 ` [PATCH 1/6] x86/mm: Thread pgprot_t through init_memory_mapping() Logan Gunthorpe
2019-12-09 19:13 ` [PATCH 2/6] x86/mm: Introduce _set_memory_prot() Logan Gunthorpe
2019-12-09 19:13 ` [PATCH 3/6] powerpc/mm: Thread pgprot_t through create_section_mapping() Logan Gunthorpe
2019-12-09 19:13 ` [PATCH 4/6] s390/mm: Thread pgprot_t through vmem_add_mapping() Logan Gunthorpe
2019-12-09 19:13 ` [PATCH 5/6] mm, memory_hotplug: Provide argument for the pgprot_t in arch_add_memory() Logan Gunthorpe
2019-12-09 19:23 ` David Hildenbrand
2019-12-09 20:24 ` Logan Gunthorpe
2019-12-09 20:41 ` Michal Hocko
2019-12-09 21:00 ` Dan Williams [this message]
2019-12-09 21:27 ` Logan Gunthorpe
2019-12-09 21:24 ` Logan Gunthorpe
2019-12-10 9:56 ` Michal Hocko
2019-12-09 20:43 ` Dan Williams
2019-12-09 20:52 ` David Hildenbrand
2019-12-10 10:04 ` Michal Hocko
2019-12-10 10:09 ` David Hildenbrand
2019-12-10 10:34 ` Michal Hocko
2019-12-10 11:25 ` David Hildenbrand
2019-12-10 23:52 ` Logan Gunthorpe
2019-12-11 8:37 ` Michal Hocko
2019-12-09 19:13 ` [PATCH 6/6] mm/memremap: Set caching mode for PCI P2PDMA memory to WC Logan Gunthorpe
2019-12-09 20:43 ` [PATCH 0/6] Allow setting caching mode in arch_add_memory() for P2PDMA Christoph Hellwig
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