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Fri, 6 Mar 2026 15:44:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772811857; bh=Irog342MSr8k0zPuW6pGzgfpJRPPfcyU46dDqhpUBU8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=cPwvk7hYBURwasb7XgxxL1kr9EppTKvwp8HXAgsivHXKjqp75sTPHdGxFMqtH5GoC KWahvwUXupdk0vP9+GXBHipHQQaevBgrSxRfLxtzes8UcuTMob+APPrkVxnMkQ43H4 pqYJhYjEEPC6KmAUY+xkMmbNui7Qj/X1BlHXLP7cxJoqraZdVLVMgU71DKUckL8hlD U99gWs8Qztv8u3kD1L8S1yKRUESqYW3qiE3m5QVefWfGRMXRXb2kxyi5TOLk2Jh50O s5ZJkDQL5uz7rygM1S6oeiYTyYKoEc7zKF2NvNddiKTezKxSMgVXGP1dArr2DxQVXv OaWe1NzgWP/6A== Message-ID: <81e7bd1c-54d5-4f88-969a-685177447c51@kernel.org> Date: Fri, 6 Mar 2026 16:44:06 +0100 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 05/13] mm/page_vma_mapped: Add flag to page_vma_mapped_walk::flags to track device private pages To: Jordan Niethe , linux-mm@kvack.org Cc: balbirs@nvidia.com, matthew.brost@intel.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, ziy@nvidia.com, apopple@nvidia.com, lorenzo.stoakes@oracle.com, lyude@redhat.com, dakr@kernel.org, airlied@gmail.com, simona@ffwll.ch, rcampbell@nvidia.com, mpenttil@redhat.com, jgg@nvidia.com, willy@infradead.org, linuxppc-dev@lists.ozlabs.org, intel-xe@lists.freedesktop.org, jgg@ziepe.ca, Felix.Kuehling@amd.com, jhubbard@nvidia.com, maddy@linux.ibm.com, mpe@ellerman.id.au, ying.huang@linux.alibaba.com References: <20260202113642.59295-1-jniethe@nvidia.com> <20260202113642.59295-6-jniethe@nvidia.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/2/26 12:36, Jordan Niethe wrote: > A future change will remove device private pages from the physical > address space. This will mean that device private pages no longer have > normal PFN and must be handled separately. > > Prepare for this by adding a PVMW_DEVICE_PRIVATE flag to > page_vma_mapped_walk::flags. This indicates that > page_vma_mapped_walk::pfn contains a device private offset rather than a > normal pfn. > > Once the device private pages are removed from the physical address > space this flag will be used to ensure a device private offset is > returned. > > Reviewed-by: Zi Yan > Signed-off-by: Jordan Niethe > Signed-off-by: Alistair Popple > --- > v1: > - Update for HMM huge page support > v2: > - Move adding device_private param to check_pmd() until final patch > v3: > - Track device private offset in pvmw::flags instead of pvmw::pfn > v4: > - No change > --- > include/linux/rmap.h | 24 ++++++++++++++++++++++-- > mm/page_vma_mapped.c | 4 ++-- > mm/rmap.c | 4 ++-- > mm/vmscan.c | 2 +- > 4 files changed, 27 insertions(+), 7 deletions(-) > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > index daa92a58585d..1b03297f13dc 100644 > --- a/include/linux/rmap.h > +++ b/include/linux/rmap.h > @@ -921,6 +921,8 @@ struct page *make_device_exclusive(struct mm_struct *mm, unsigned long addr, > #define PVMW_SYNC (1 << 0) > /* Look for migration entries rather than present PTEs */ > #define PVMW_MIGRATION (1 << 1) > +/* pvmw::pfn is a device private offset */ > +#define PVMW_DEVICE_PRIVATE (1 << 2) > > /* Result flags */ > > @@ -939,14 +941,32 @@ struct page_vma_mapped_walk { > unsigned int flags; > }; > > +static inline unsigned long page_vma_walk_flags(const struct folio *folio, > + unsigned long flags) > +{ > + if (folio_is_device_private(folio)) > + return flags | PVMW_DEVICE_PRIVATE; > + return flags; > +} > + > +static inline unsigned long folio_page_vma_walk_pfn(const struct folio *folio) > +{ > + return folio_pfn(folio); > +} > + > +static inline struct folio *page_vma_walk_pfn_to_folio(struct page_vma_mapped_walk *pvmw) > +{ > + return pfn_folio(pvmw->pfn); > +} > + > #define DEFINE_FOLIO_VMA_WALK(name, _folio, _vma, _address, _flags) \ > struct page_vma_mapped_walk name = { \ > - .pfn = folio_pfn(_folio), \ > + .pfn = folio_page_vma_walk_pfn(_folio), \ > .nr_pages = folio_nr_pages(_folio), \ > .pgoff = folio_pgoff(_folio), \ > .vma = _vma, \ > .address = _address, \ > - .flags = _flags, \ > + .flags = page_vma_walk_flags(_folio, _flags), \ > } That's all rather horrible ... I was asking myself recently, why something that is called "page_vma_mapped_walk" consume a pfn. It's just a horrible interface. * DEFINE_FOLIO_VMA_WALK() users obviously receive a folio. * mm/migrate_device.c just abuses page_vma_mapped_walk() to make set_pmd_migration_entry() work. But we have a folio. * page_mapped_in_vma() has a page/folio. mapping_wrprotect_range_one() and pfn_mkclean_range() are the real issues. They all end up calling page_vma_mkclean_one(), which does not operate on pages/folios. Ideally, the odd pfn case would use it's own simplified infrastructure. So, could we simply add a folio+page pointer in case we have one, and use that one if set, leaving leaving the pfn unset? Then, the pfn would only be set for the mapping_wrprotect_range_one/pfn_mkclean_range case. I don't think device-private folios would ever have to mess with that. Then, you just always have a folio+page and don't even have to worry about the pfn? -- Cheers, David