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(p200300d82f20da00b70ad5023b511f2d.dip0.t-ipconnect.de. [2003:d8:2f20:da00:b70a:d502:3b51:1f2d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45e0372b983sm53570065e9.9.2025.09.12.01.41.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Sep 2025 01:41:11 -0700 (PDT) Message-ID: <04d2d781-fd5e-4778-b042-d4dbeb8c5d49@redhat.com> Date: Fri, 12 Sep 2025 10:41:10 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 1/5] mm: softdirty: Add pgtable_soft_dirty_supported() To: Chunyan Zhang Cc: Chunyan Zhang , linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Deepak Gupta , Ved Shanbhogue , Alexander Viro , Christian Brauner , Jan Kara , Andrew Morton , Peter Xu , Arnd Bergmann , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Axel Rasmussen , Yuanchu Xie References: <20250911095602.1130290-1-zhangchunyan@iscas.ac.cn> <20250911095602.1130290-2-zhangchunyan@iscas.ac.cn> <9bcaf3ec-c0a1-4ca5-87aa-f84e297d1e42@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit [...] >>> +/* >>> + * We should remove the VM_SOFTDIRTY flag if the soft-dirty bit is >>> + * unavailable on which the kernel is running, even if the architecture >>> + * provides the resource and soft-dirty is compiled in. >>> + */ >>> +#ifdef CONFIG_MEM_SOFT_DIRTY >>> + if (!pgtable_soft_dirty_supported()) >>> + mnemonics[ilog2(VM_SOFTDIRTY)][0] = 0; >>> +#endif >> >> You can now drop the ifdef. > > Ok, you mean define VM_SOFTDIRTY 0x08000000 no matter if > MEM_SOFT_DIRTY is compiled in, right? > > Then I need memcpy() to set mnemonics[ilog2(VM_SOFTDIRTY)] here. The whole hunk will not be required when we make sure VM_SOFTDIRTY never gets set, correct? > >> >> But, I wonder if could we instead just stop setting the flag. Then we don't >> have to worry about any VM_SOFTDIRTY checks. >> >> Something like the following >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 892fe5dbf9de0..8b8bf63a32ef7 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -783,6 +783,7 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm) >> static inline void vm_flags_init(struct vm_area_struct *vma, >> vm_flags_t flags) >> { >> + VM_WARN_ON_ONCE(!pgtable_soft_dirty_supported() && (flags & VM_SOFTDIRTY)); >> ACCESS_PRIVATE(vma, __vm_flags) = flags; >> } >> >> @@ -801,6 +802,7 @@ static inline void vm_flags_reset(struct vm_area_struct *vma, >> static inline void vm_flags_reset_once(struct vm_area_struct *vma, >> vm_flags_t flags) >> { >> + VM_WARN_ON_ONCE(!pgtable_soft_dirty_supported() && (flags & VM_SOFTDIRTY)); >> vma_assert_write_locked(vma); >> WRITE_ONCE(ACCESS_PRIVATE(vma, __vm_flags), flags); >> } >> @@ -808,6 +810,7 @@ static inline void vm_flags_reset_once(struct vm_area_struct *vma, >> static inline void vm_flags_set(struct vm_area_struct *vma, >> vm_flags_t flags) >> { >> + VM_WARN_ON_ONCE(!pgtable_soft_dirty_supported() && (flags & VM_SOFTDIRTY)); >> vma_start_write(vma); >> ACCESS_PRIVATE(vma, __vm_flags) |= flags; >> } >> diff --git a/mm/mmap.c b/mm/mmap.c >> index 5fd3b80fda1d5..40cb3fbf9a247 100644 >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -1451,8 +1451,10 @@ static struct vm_area_struct *__install_special_mapping( >> return ERR_PTR(-ENOMEM); >> >> vma_set_range(vma, addr, addr + len, 0); >> - vm_flags_init(vma, (vm_flags | mm->def_flags | >> - VM_DONTEXPAND | VM_SOFTDIRTY) & ~VM_LOCKED_MASK); >> + vm_flags |= mm->def_flags | VM_DONTEXPAND; > > Why use '|=' rather than not directly setting vm_flags which is an > uninitialized variable? vm_flags is passed in by the caller? But just to clarify: this code was just a quick hack, adjust it as you need. [...] >>> >>> + if (!pgtable_soft_dirty_supported()) >>> + return; >>> + >>> if (pmd_present(pmd)) { >>> /* See comment in change_huge_pmd() */ >>> old = pmdp_invalidate(vma, addr, pmdp); >> >> That would all be handled with the above never-set-VM_SOFTDIRTY. I meant that there is no need to add the pgtable_soft_dirty_supported() check. > > Sorry I'm not sure I understand here, you mean no longer need #ifdef > CONFIG_MEM_SOFT_DIRTY for these function definitions, right? Likely we could drop them. VM_SOFTDIRTY will never be set so the code will not be invoked. And for architectures where VM_SOFTDIRTY is never even possible (!CONFIG_MEM_SOFT_DIRTY) we keep it as 0. That way, the compiler can even optimize out all of that code because "vma->vm_flags & VM_SOFTDIRTY" -> "vma->vm_flags & 0" will never be true. > >> >>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h >>> index 4c035637eeb7..2a3578a4ae4c 100644 >>> --- a/include/linux/pgtable.h >>> +++ b/include/linux/pgtable.h >>> @@ -1537,6 +1537,18 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot) >>> #define arch_start_context_switch(prev) do {} while (0) >>> #endif >>> >>> +/* >>> + * Some platforms can customize the PTE soft-dirty bit making it unavailable >>> + * even if the architecture provides the resource. >>> + * Adding this API allows architectures to add their own checks for the >>> + * devices on which the kernel is running. >>> + * Note: When overiding it, please make sure the CONFIG_MEM_SOFT_DIRTY >>> + * is part of this macro. >>> + */ >>> +#ifndef pgtable_soft_dirty_supported >>> +#define pgtable_soft_dirty_supported() IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) >>> +#endif >>> + >>> #ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY >>> #ifndef CONFIG_ARCH_ENABLE_THP_MIGRATION >>> static inline pmd_t pmd_swp_mksoft_dirty(pmd_t pmd) >>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c >>> index 830107b6dd08..b32ce2b0b998 100644 >>> --- a/mm/debug_vm_pgtable.c >>> +++ b/mm/debug_vm_pgtable.c >>> @@ -690,7 +690,7 @@ static void __init pte_soft_dirty_tests(struct pgtable_debug_args *args) >>> { >>> pte_t pte = pfn_pte(args->fixed_pte_pfn, args->page_prot); >>> >>> - if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY)) >>> + if (!pgtable_soft_dirty_supported()) >>> return; >>> >>> pr_debug("Validating PTE soft dirty\n"); >>> @@ -702,7 +702,7 @@ static void __init pte_swap_soft_dirty_tests(struct pgtable_debug_args *args) >>> { >>> pte_t pte; >>> >>> - if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY)) >>> + if (!pgtable_soft_dirty_supported()) >>> return; >>> >>> pr_debug("Validating PTE swap soft dirty\n"); >>> @@ -718,7 +718,7 @@ static void __init pmd_soft_dirty_tests(struct pgtable_debug_args *args) >>> { >>> pmd_t pmd; >>> >>> - if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY)) >>> + if (!pgtable_soft_dirty_supported()) >>> return; >>> >>> if (!has_transparent_hugepage()) >>> @@ -734,8 +734,8 @@ static void __init pmd_swap_soft_dirty_tests(struct pgtable_debug_args *args) >>> { >>> pmd_t pmd; >>> >>> - if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) || >>> - !IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION)) >>> + if (!pgtable_soft_dirty_supported() || >>> + !IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION)) >>> return; >>> >>> if (!has_transparent_hugepage()) >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index 9c38a95e9f09..218d430a2ec6 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -2271,12 +2271,13 @@ static inline int pmd_move_must_withdraw(spinlock_t *new_pmd_ptl, >>> >>> static pmd_t move_soft_dirty_pmd(pmd_t pmd) >>> { >>> -#ifdef CONFIG_MEM_SOFT_DIRTY >>> - if (unlikely(is_pmd_migration_entry(pmd))) >>> - pmd = pmd_swp_mksoft_dirty(pmd); >>> - else if (pmd_present(pmd)) >>> - pmd = pmd_mksoft_dirty(pmd); >>> -#endif >>> + if (pgtable_soft_dirty_supported()) { >>> + if (unlikely(is_pmd_migration_entry(pmd))) >>> + pmd = pmd_swp_mksoft_dirty(pmd); >>> + else if (pmd_present(pmd)) >>> + pmd = pmd_mksoft_dirty(pmd); >>> + } >>> + >> >> Wondering, should simply the arch take care of that and we can just clal >> pmd_swp_mksoft_dirty / pmd_mksoft_dirty? > I think we have that already in include/linux/pgtable.h: We have stubs that just don't do anything. For riscv support you would handle runtime-enablement in these helpers. > >> >>> return pmd; >>> } >>> >>> diff --git a/mm/internal.h b/mm/internal.h >>> index 45b725c3dc03..c6ca62f8ecf3 100644 >>> --- a/mm/internal.h >>> +++ b/mm/internal.h >>> @@ -1538,7 +1538,7 @@ static inline bool vma_soft_dirty_enabled(struct vm_area_struct *vma) >>> * VM_SOFTDIRTY is defined as 0x0, then !(vm_flags & VM_SOFTDIRTY) >>> * will be constantly true. >>> */ >>> - if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY)) >>> + if (!pgtable_soft_dirty_supported()) >>> return false; >>> >> >> That should be handled with the above never-set-VM_SOFTDIRTY. > > We don't need to check if (!pgtable_soft_dirty_supported()) if I > understand correctly. Hm, let me think about that. No, I think this has to stay as the comment says, so this case here is special. -- Cheers David / dhildenb