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[2003:d8:2f31:700:3851:c66a:b6b9:3490]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568b79f45sm13384674f8f.101.2025.06.17.02.30.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Jun 2025 02:30:22 -0700 (PDT) Message-ID: Date: Tue, 17 Jun 2025 11:30:20 +0200 Precedence: bulk X-Mailing-List: nvdimm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 02/14] mm: Filter zone device pages returned from folio_walk_start() From: David Hildenbrand 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 References: <11dd5b70546ec67593a4bf79f087b113f15d6bb1.1750075065.git-series.apopple@nvidia.com> <6afc2e67-3ecb-41a5-9c8f-00ecd64f035a@redhat.com> Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17.06.25 11:25, David Hildenbrand wrote: > On 16.06.25 13:58, Alistair Popple wrote: >> Previously dax pages were skipped by the pagewalk code as pud_special() or >> vm_normal_page{_pmd}() would be false for DAX pages. Now that dax pages are >> refcounted normally that is no longer the case, so the pagewalk code will >> start returning them. >> >> Most callers already explicitly filter for DAX or zone device pages so >> don't need updating. However some don't, so add checks to those callers. >> >> Signed-off-by: Alistair Popple >> >> --- >> >> Changes since v1: >> >> - Dropped "mm/pagewalk: Skip dax pages in pagewalk" and replaced it >> with this new patch for v2 >> >> - As suggested by David and Jason we can filter the folios in the >> callers instead of doing it in folio_start_walk(). Most callers >> already do this (see below). >> >> I audited all callers of folio_walk_start() and found the following: >> >> mm/ksm.c: >> >> break_ksm() - doesn't need to filter zone_device pages because the can >> never be KSM pages. >> >> get_mergeable_page() - already filters out zone_device pages. >> scan_get_next_rmap_iterm() - already filters out zone_device_pages. >> >> mm/huge_memory.c: >> >> split_huge_pages_pid() - already checks for DAX with >> vma_not_suitable_for_thp_split() >> >> mm/rmap.c: >> >> make_device_exclusive() - only works on anonymous pages, although >> there'd be no issue with finding a DAX page even if support was extended >> to file-backed pages. >> >> mm/migrate.c: >> >> add_folio_for_migration() - already checks the vma with vma_migratable() >> do_pages_stat_array() - explicitly checks for zone_device folios >> >> kernel/event/uprobes.c: >> >> uprobe_write_opcode() - only works on anonymous pages, not sure if >> zone_device could ever work so add an explicit check >> >> arch/s390/mm/fault.c: >> >> do_secure_storage_access() - not sure so be conservative and add a check >> >> arch/s390/kernel/uv.c: >> >> make_hva_secure() - not sure so be conservative and add a check >> --- >> arch/s390/kernel/uv.c | 2 +- >> arch/s390/mm/fault.c | 2 +- >> kernel/events/uprobes.c | 2 +- >> 3 files changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c >> index b99478e..55aa280 100644 >> --- a/arch/s390/kernel/uv.c >> +++ b/arch/s390/kernel/uv.c >> @@ -424,7 +424,7 @@ int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header >> return -EFAULT; >> } >> folio = folio_walk_start(&fw, vma, hva, 0); >> - if (!folio) { >> + if (!folio || folio_is_zone_device(folio)) { >> mmap_read_unlock(mm); >> return -ENXIO; >> } >> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c >> index e1ad05b..df1a067 100644 >> --- a/arch/s390/mm/fault.c >> +++ b/arch/s390/mm/fault.c >> @@ -449,7 +449,7 @@ void do_secure_storage_access(struct pt_regs *regs) >> if (!vma) >> return handle_fault_error(regs, SEGV_MAPERR); >> folio = folio_walk_start(&fw, vma, addr, 0); >> - if (!folio) { >> + if (!folio || folio_is_zone_device(folio)) { >> mmap_read_unlock(mm); >> return; >> } > > Curious, does s390 even support ZONE_DEVICE and could trigger this? Ah, I see you raised this above. Even if it could be triggered (which I don't think), I wonder if there would actually be a problem with zone_device folios in here? I think these two can be dropped for now -- Cheers, David / dhildenb