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Date: Wed, 8 Jan 2020 10:17:10 -0700
From: Logan Gunthorpe <logang@...tatee.com>
To: David Hildenbrand <david@...hat.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 v2 7/8] mm/memory_hotplug: Add pgprot_t to mhp_modifiers
On 2020-01-08 5:39 a.m., David Hildenbrand wrote:
> On 07.01.20 21:59, 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.
>
> You're adding a parameter indirectly by adding it to the structure.
> Maybe "provide a way to specify the pgprot value explicitly to
> arch_add_memory()"
>
>>
>> Of the arches that support MEMORY_HOTPLUG: x86_64, s390 and arm64 is a
>
> s/is/need/
>
>> 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
>
> "page table protection" ?
>
>> 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 | 3 ++-
>> arch/ia64/mm/init.c | 4 ++++
>> arch/powerpc/mm/mem.c | 3 ++-
>> arch/s390/mm/init.c | 2 +-
>> 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 | 2 +-
>> mm/memremap.c | 6 +++---
>> 10 files changed, 24 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index 3320406579c3..9b214b0d268f 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, modifiers->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 daf438e08b96..5fd6ae4929c9 100644
>> --- a/arch/ia64/mm/init.c
>> +++ b/arch/ia64/mm/init.c
>> @@ -677,6 +677,10 @@ int arch_add_memory(int nid, u64 start, u64 size,
>> int ret;
>>
>> ret = __add_pages(nid, start_pfn, nr_pages, modifiers);
>> + if (modifiers->pgprot != PAGE_KERNEL)
>> + return -EINVAL;
>
> ... maybe better "if (WARN_ON_ONCE(...))"
> [...]
>
>> --- a/include/linux/memory_hotplug.h
>> +++ b/include/linux/memory_hotplug.h
>> @@ -56,9 +56,11 @@ enum {
>> /*
>> * Restrictions for the memory hotplug:
>> * altmap: alternative allocator for memmap array
>> + * pgprot: page protection flags to apply to newly added page tables
>> */
>> struct mhp_modifiers {
>> struct vmem_altmap *altmap;
>> + pgprot_t pgprot;
>> };
>>
>> /*
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 1bb3f92e087d..0888f821af06 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1027,7 +1027,7 @@ static int online_memory_block(struct memory_block *mem, void *arg)
>> */
>> int __ref add_memory_resource(int nid, struct resource *res)
>> {
>> - struct mhp_modifiers modifiers = {};
>> + struct mhp_modifiers modifiers = {.pgprot = PAGE_KERNEL};
>
> I think we usually use spaces like
>
> = { .pgprot = PAGE_KERNEL };
>
> t480s: ~/git/linux virtio-mem-v1 $ git grep "= {\." | wc -l
> 978
> t480s: ~/git/linux virtio-mem-v1 $ git grep "= { " | wc -l
> 35447
>
>> u64 start, size;
>> bool new_node = false;
>> int ret;
>> diff --git a/mm/memremap.c b/mm/memremap.c
>> index e30be8ba706b..45ab4ef0643d 100644
>> --- a/mm/memremap.c
>> +++ b/mm/memremap.c
>> @@ -163,8 +163,8 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
>> * We do not want any optional features only our own memmap
>> */
>> .altmap = pgmap_altmap(pgmap),
>> + .pgprot = PAGE_KERNEL,
>> };
>> - pgprot_t pgprot = PAGE_KERNEL;
>> int error, is_ram;
>> bool need_devmap_managed = true;
>>
>> @@ -252,8 +252,8 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
>> if (nid < 0)
>> nid = numa_mem_id();
>>
>> - error = track_pfn_remap(NULL, &pgprot, PHYS_PFN(res->start), 0,
>> - resource_size(res));
>> + error = track_pfn_remap(NULL, &modifiers.pgprot, PHYS_PFN(res->start),
>> + 0, resource_size(res));
>> if (error)
>> goto err_pfn_remap;
>>
>>
>
> The !arch code looks good to me (besides I would prefer "params" instead
> of "modifiers").
>
> Acked-by: David Hildenbrand <david@...hat.com>
Thanks, I'll make the changes above for v3.
Logan
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