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[2003:d8:2f31:700:3851:c66a:b6b9:3490]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4532e13d014sm171119765e9.24.2025.06.17.02.49.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Jun 2025 02:49:05 -0700 (PDT) Message-ID: <1709a271-273b-4668-b813-648e5785e4e8@redhat.com> Date: Tue, 17 Jun 2025 11:49:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 03/14] mm: Convert vmf_insert_mixed() from using pte_devmap to pte_special To: Alistair Popple , akpm@linux-foundation.org Cc: linux-mm@kvack.org, gerald.schaefer@linux.ibm.com, dan.j.williams@intel.com, jgg@ziepe.ca, willy@infradead.org, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, zhang.lyra@gmail.com, debug@rivosinc.com, bjorn@kernel.org, balbirs@nvidia.com, lorenzo.stoakes@oracle.com, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-cxl@vger.kernel.org, dri-devel@lists.freedesktop.org, John@Groves.net, m.szyprowski@samsung.com, Jason Gunthorpe References: <5c03174d2ea76f579e4675f5fab6277f5dd91be2.1750075065.git-series.apopple@nvidia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 5E6F5100008 X-Stat-Signature: 81imqjgc5khbmrxqh915t9scxju3t55m X-HE-Tag: 1750153749-221502 X-HE-Meta: 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 tb1v5jtg 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 16.06.25 13:58, Alistair Popple wrote: > DAX no longer requires device PTEs as it always has a ZONE_DEVICE page > associated with the PTE that can be reference counted normally. Other users > of pte_devmap are drivers that set PFN_DEV when calling vmf_insert_mixed() > which ensures vm_normal_page() returns NULL for these entries. > > There is no reason to distinguish these pte_devmap users so in order to > free up a PTE bit use pte_special instead for entries created with > vmf_insert_mixed(). This will ensure vm_normal_page() will continue to > return NULL for these pages. > > Architectures that don't support pte_special also don't support pte_devmap > so those will continue to rely on pfn_valid() to determine if the page can > be mapped. > > Signed-off-by: Alistair Popple > Reviewed-by: Jason Gunthorpe > Reviewed-by: Dan Williams > --- > mm/hmm.c | 3 --- > mm/memory.c | 20 ++------------------ > mm/vmscan.c | 2 +- > 3 files changed, 3 insertions(+), 22 deletions(-) > > diff --git a/mm/hmm.c b/mm/hmm.c > index 5311753..1a3489f 100644 > --- a/mm/hmm.c > +++ b/mm/hmm.c > @@ -302,13 +302,10 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, > goto fault; > > /* > - * Bypass devmap pte such as DAX page when all pfn requested > - * flags(pfn_req_flags) are fulfilled. > * Since each architecture defines a struct page for the zero page, just > * fall through and treat it like a normal page. > */ > if (!vm_normal_page(walk->vma, addr, pte) && > - !pte_devmap(pte) && > !is_zero_pfn(pte_pfn(pte))) { > if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) { > pte_unmap(ptep); > diff --git a/mm/memory.c b/mm/memory.c > index b0cda5a..2c6eda1 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -598,16 +598,6 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, > return NULL; > if (is_zero_pfn(pfn)) > return NULL; > - if (pte_devmap(pte)) > - /* > - * NOTE: New users of ZONE_DEVICE will not set pte_devmap() > - * and will have refcounts incremented on their struct pages > - * when they are inserted into PTEs, thus they are safe to > - * return here. Legacy ZONE_DEVICE pages that set pte_devmap() > - * do not have refcounts. Example of legacy ZONE_DEVICE is > - * MEMORY_DEVICE_FS_DAX type in pmem or virtio_fs drivers. > - */ > - return NULL; > > print_bad_pte(vma, addr, pte, NULL); > return NULL; > @@ -2483,10 +2473,7 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr, > } > > /* Ok, finally just insert the thing.. */ > - if (pfn_t_devmap(pfn)) > - entry = pte_mkdevmap(pfn_t_pte(pfn, prot)); > - else > - entry = pte_mkspecial(pfn_t_pte(pfn, prot)); > + entry = pte_mkspecial(pfn_t_pte(pfn, prot)); > > if (mkwrite) { > entry = pte_mkyoung(entry); > @@ -2597,8 +2584,6 @@ static bool vm_mixed_ok(struct vm_area_struct *vma, pfn_t pfn, bool mkwrite) > /* these checks mirror the abort conditions in vm_normal_page */ > if (vma->vm_flags & VM_MIXEDMAP) > return true; > - if (pfn_t_devmap(pfn)) > - return true; > if (pfn_t_special(pfn)) > return true; > if (is_zero_pfn(pfn_t_to_pfn(pfn))) > @@ -2630,8 +2615,7 @@ static vm_fault_t __vm_insert_mixed(struct vm_area_struct *vma, > * than insert_pfn). If a zero_pfn were inserted into a VM_MIXEDMAP > * without pte special, it would there be refcounted as a normal page. > */ > - if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) && > - !pfn_t_devmap(pfn) && pfn_t_valid(pfn)) { > + if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) && pfn_t_valid(pfn)) { > struct page *page; > > /* > diff --git a/mm/vmscan.c b/mm/vmscan.c > index a93a1ba..85bf782 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3424,7 +3424,7 @@ static unsigned long get_pte_pfn(pte_t pte, struct vm_area_struct *vma, unsigned > if (!pte_present(pte) || is_zero_pfn(pfn)) > return -1; > > - if (WARN_ON_ONCE(pte_devmap(pte) || pte_special(pte))) > + if (WARN_ON_ONCE(pte_special(pte))) > return -1; > > if (!pte_young(pte) && !mm_has_notifiers(vma->vm_mm)) -- Cheers, David / dhildenb