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(p200300d82f4d1a004fdf53e21a36ba34.dip0.t-ipconnect.de. [2003:d8:2f4d:1a00:4fdf:53e2:1a36:ba34]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a1f5a4bbf0sm15453834f8f.82.2025.05.13.03.22.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 May 2025 03:22:46 -0700 (PDT) Message-ID: <148ed54a-d34d-4ffc-9de4-467cd996af32@redhat.com> Date: Tue, 13 May 2025 12:22:45 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 04/11] mm: convert VM_PFNMAP tracking to pfnmap_track() + pfnmap_untrack() To: Lorenzo Stoakes Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-trace-kernel@vger.kernel.org, Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Simona Vetter , Andrew Morton , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , Peter Xu , Ingo Molnar References: <20250512123424.637989-1-david@redhat.com> <20250512123424.637989-5-david@redhat.com> <8d96176d-f36b-4714-9780-6131c8470f50@lucifer.local> From: David Hildenbrand 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <8d96176d-f36b-4714-9780-6131c8470f50@lucifer.local> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: X6xdHmB-vhDGDWgCQxsMwbpgcCsjiUMfbkyBZlxZBw4_1747131768 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 13.05.25 12:16, Lorenzo Stoakes wrote: > On Tue, May 13, 2025 at 11:10:45AM +0200, David Hildenbrand wrote: >> On 12.05.25 18:42, Lorenzo Stoakes wrote: >>> On Mon, May 12, 2025 at 02:34:17PM +0200, David Hildenbrand wrote: >>>> Let's use our new interface. In remap_pfn_range(), we'll now decide >>>> whether we have to track (full VMA covered) or only lookup the >>>> cachemode (partial VMA covered). >>>> >>>> Remember what we have to untrack by linking it from the VMA. When >>>> duplicating VMAs (e.g., splitting, mremap, fork), we'll handle it similar >>>> to anon VMA names, and use a kref to share the tracking. >>>> >>>> Once the last VMA un-refs our tracking data, we'll do the untracking, >>>> which simplifies things a lot and should sort our various issues we saw >>>> recently, for example, when partially unmapping/zapping a tracked VMA. >>>> >>>> This change implies that we'll keep tracking the original PFN range even >>>> after splitting + partially unmapping it: not too bad, because it was >>>> not working reliably before. The only thing that kind-of worked before >>>> was shrinking such a mapping using mremap(): we managed to adjust the >>>> reservation in a hacky way, now we won't adjust the reservation but >>>> leave it around until all involved VMAs are gone. >>>> >>>> If that ever turns out to be an issue, we could hook into VM splitting >>>> code and split the tracking; however, that adds complexity that might >>>> not be required, so we'll keep it simple for now. >>>> >>>> Acked-by: Ingo Molnar # x86 bits >>>> Signed-off-by: David Hildenbrand >>> >>> Other than small nit below, >>> >>> Reviewed-by: Lorenzo Stoakes >>> >>>> --- >>>> include/linux/mm_inline.h | 2 + >>>> include/linux/mm_types.h | 11 ++++++ >>>> mm/memory.c | 82 +++++++++++++++++++++++++++++++-------- >>>> mm/mmap.c | 5 --- >>>> mm/mremap.c | 4 -- >>>> mm/vma_init.c | 50 ++++++++++++++++++++++++ >>>> 6 files changed, 129 insertions(+), 25 deletions(-) >>>> >>>> diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h >>>> index f9157a0c42a5c..89b518ff097e6 100644 >>>> --- a/include/linux/mm_inline.h >>>> +++ b/include/linux/mm_inline.h >>>> @@ -447,6 +447,8 @@ static inline bool anon_vma_name_eq(struct anon_vma_name *anon_name1, >>>> >>>> #endif /* CONFIG_ANON_VMA_NAME */ >>>> >>>> +void pfnmap_track_ctx_release(struct kref *ref); >>>> + >>>> static inline void init_tlb_flush_pending(struct mm_struct *mm) >>>> { >>>> atomic_set(&mm->tlb_flush_pending, 0); >>>> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h >>>> index 15808cad2bc1a..3e934dc6057c4 100644 >>>> --- a/include/linux/mm_types.h >>>> +++ b/include/linux/mm_types.h >>>> @@ -763,6 +763,14 @@ struct vma_numab_state { >>>> int prev_scan_seq; >>>> }; >>>> >>>> +#ifdef __HAVE_PFNMAP_TRACKING >>>> +struct pfnmap_track_ctx { >>>> + struct kref kref; >>>> + unsigned long pfn; >>>> + unsigned long size; /* in bytes */ >>>> +}; >>>> +#endif >>>> + >>>> /* >>>> * Describes a VMA that is about to be mmap()'ed. Drivers may choose to >>>> * manipulate mutable fields which will cause those fields to be updated in the >>>> @@ -900,6 +908,9 @@ struct vm_area_struct { >>>> struct anon_vma_name *anon_name; >>>> #endif >>>> struct vm_userfaultfd_ctx vm_userfaultfd_ctx; >>>> +#ifdef __HAVE_PFNMAP_TRACKING >>>> + struct pfnmap_track_ctx *pfnmap_track_ctx; >>>> +#endif >>>> } __randomize_layout; >>>> >>>> #ifdef CONFIG_NUMA >>>> diff --git a/mm/memory.c b/mm/memory.c >>>> index 064fc55d8eab9..4cf4adb0de266 100644 >>>> --- a/mm/memory.c >>>> +++ b/mm/memory.c >>>> @@ -1371,7 +1371,7 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) >>>> struct mm_struct *dst_mm = dst_vma->vm_mm; >>>> struct mm_struct *src_mm = src_vma->vm_mm; >>>> struct mmu_notifier_range range; >>>> - unsigned long next, pfn = 0; >>>> + unsigned long next; >>>> bool is_cow; >>>> int ret; >>>> >>>> @@ -1381,12 +1381,6 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) >>>> if (is_vm_hugetlb_page(src_vma)) >>>> return copy_hugetlb_page_range(dst_mm, src_mm, dst_vma, src_vma); >>>> >>>> - if (unlikely(src_vma->vm_flags & VM_PFNMAP)) { >>>> - ret = track_pfn_copy(dst_vma, src_vma, &pfn); >>>> - if (ret) >>>> - return ret; >>>> - } >>>> - >>>> /* >>>> * We need to invalidate the secondary MMU mappings only when >>>> * there could be a permission downgrade on the ptes of the >>>> @@ -1428,8 +1422,6 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) >>>> raw_write_seqcount_end(&src_mm->write_protect_seq); >>>> mmu_notifier_invalidate_range_end(&range); >>>> } >>>> - if (ret && unlikely(src_vma->vm_flags & VM_PFNMAP)) >>>> - untrack_pfn_copy(dst_vma, pfn); >>>> return ret; >>>> } >>>> >>>> @@ -1924,9 +1916,6 @@ static void unmap_single_vma(struct mmu_gather *tlb, >>>> if (vma->vm_file) >>>> uprobe_munmap(vma, start, end); >>>> >>>> - if (unlikely(vma->vm_flags & VM_PFNMAP)) >>>> - untrack_pfn(vma, 0, 0, mm_wr_locked); >>>> - >>>> if (start != end) { >>>> if (unlikely(is_vm_hugetlb_page(vma))) { >>>> /* >>>> @@ -2872,6 +2861,36 @@ int remap_pfn_range_notrack(struct vm_area_struct *vma, unsigned long addr, >>>> return error; >>>> } >>>> >>>> +#ifdef __HAVE_PFNMAP_TRACKING >>>> +static inline struct pfnmap_track_ctx *pfnmap_track_ctx_alloc(unsigned long pfn, >>>> + unsigned long size, pgprot_t *prot) >>>> +{ >>>> + struct pfnmap_track_ctx *ctx; >>>> + >>>> + if (pfnmap_track(pfn, size, prot)) >>>> + return ERR_PTR(-EINVAL); >>>> + >>>> + ctx = kmalloc(sizeof(*ctx), GFP_KERNEL); >>>> + if (unlikely(!ctx)) { >>>> + pfnmap_untrack(pfn, size); >>>> + return ERR_PTR(-ENOMEM); >>>> + } >>>> + >>>> + ctx->pfn = pfn; >>>> + ctx->size = size; >>>> + kref_init(&ctx->kref); >>>> + return ctx; >>>> +} >>>> + >>>> +void pfnmap_track_ctx_release(struct kref *ref) >>>> +{ >>>> + struct pfnmap_track_ctx *ctx = container_of(ref, struct pfnmap_track_ctx, kref); >>>> + >>>> + pfnmap_untrack(ctx->pfn, ctx->size); >>>> + kfree(ctx); >>>> +} >>>> +#endif /* __HAVE_PFNMAP_TRACKING */ >>>> + >>>> /** >>>> * remap_pfn_range - remap kernel memory to userspace >>>> * @vma: user vma to map to >>>> @@ -2884,20 +2903,51 @@ int remap_pfn_range_notrack(struct vm_area_struct *vma, unsigned long addr, >>>> * >>>> * Return: %0 on success, negative error code otherwise. >>>> */ >>>> +#ifdef __HAVE_PFNMAP_TRACKING >>>> int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr, >>>> unsigned long pfn, unsigned long size, pgprot_t prot) >>>> { >>>> + struct pfnmap_track_ctx *ctx = NULL; >>>> int err; >>>> >>>> - err = track_pfn_remap(vma, &prot, pfn, addr, PAGE_ALIGN(size)); >>>> - if (err) >>>> + size = PAGE_ALIGN(size); >>>> + >>>> + /* >>>> + * If we cover the full VMA, we'll perform actual tracking, and >>>> + * remember to untrack when the last reference to our tracking >>>> + * context from a VMA goes away. We'll keep tracking the whole pfn >>>> + * range even during VMA splits and partial unmapping. >>>> + * >>>> + * If we only cover parts of the VMA, we'll only setup the cachemode >>>> + * in the pgprot for the pfn range. >>>> + */ >>>> + if (addr == vma->vm_start && addr + size == vma->vm_end) { >>>> + if (vma->pfnmap_track_ctx) >>>> + return -EINVAL; >>>> + ctx = pfnmap_track_ctx_alloc(pfn, size, &prot); >>>> + if (IS_ERR(ctx)) >>>> + return PTR_ERR(ctx); >>>> + } else if (pfnmap_setup_cachemode(pfn, size, &prot)) { >>>> return -EINVAL; >>>> + } >>>> >>>> err = remap_pfn_range_notrack(vma, addr, pfn, size, prot); >>>> - if (err) >>>> - untrack_pfn(vma, pfn, PAGE_ALIGN(size), true); >>>> + if (ctx) { >>>> + if (err) >>>> + kref_put(&ctx->kref, pfnmap_track_ctx_release); >>>> + else >>>> + vma->pfnmap_track_ctx = ctx; >>>> + } >>>> return err; >>>> } >>>> + >>>> +#else >>>> +int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr, >>>> + unsigned long pfn, unsigned long size, pgprot_t prot) >>>> +{ >>>> + return remap_pfn_range_notrack(vma, addr, pfn, size, prot); >>>> +} >>>> +#endif >>>> EXPORT_SYMBOL(remap_pfn_range); >>>> >>>> /** >>>> diff --git a/mm/mmap.c b/mm/mmap.c >>>> index 50f902c08341a..09c563c951123 100644 >>>> --- a/mm/mmap.c >>>> +++ b/mm/mmap.c >>>> @@ -1784,11 +1784,6 @@ __latent_entropy int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm) >>>> tmp = vm_area_dup(mpnt); >>>> if (!tmp) >>>> goto fail_nomem; >>>> - >>>> - /* track_pfn_copy() will later take care of copying internal state. */ >>>> - if (unlikely(tmp->vm_flags & VM_PFNMAP)) >>>> - untrack_pfn_clear(tmp); >>>> - >>>> retval = vma_dup_policy(mpnt, tmp); >>>> if (retval) >>>> goto fail_nomem_policy; >>>> diff --git a/mm/mremap.c b/mm/mremap.c >>>> index 7db9da609c84f..6e78e02f74bd3 100644 >>>> --- a/mm/mremap.c >>>> +++ b/mm/mremap.c >>>> @@ -1191,10 +1191,6 @@ static int copy_vma_and_data(struct vma_remap_struct *vrm, >>>> if (is_vm_hugetlb_page(vma)) >>>> clear_vma_resv_huge_pages(vma); >>>> >>>> - /* Tell pfnmap has moved from this vma */ >>>> - if (unlikely(vma->vm_flags & VM_PFNMAP)) >>>> - untrack_pfn_clear(vma); >>>> - >>>> *new_vma_ptr = new_vma; >>>> return err; >>>> } >>>> diff --git a/mm/vma_init.c b/mm/vma_init.c >>>> index 967ca85179864..8e53c7943561e 100644 >>>> --- a/mm/vma_init.c >>>> +++ b/mm/vma_init.c >>>> @@ -71,7 +71,51 @@ static void vm_area_init_from(const struct vm_area_struct *src, >>>> #ifdef CONFIG_NUMA >>>> dest->vm_policy = src->vm_policy; >>>> #endif >>>> +#ifdef __HAVE_PFNMAP_TRACKING >>>> + dest->pfnmap_track_ctx = NULL; >>>> +#endif >>>> +} >>>> + >>>> +#ifdef __HAVE_PFNMAP_TRACKING >>>> +static inline int vma_pfnmap_track_ctx_dup(struct vm_area_struct *orig, >>>> + struct vm_area_struct *new) >>>> +{ >>>> + struct pfnmap_track_ctx *ctx = orig->pfnmap_track_ctx; >>>> + >>>> + if (likely(!ctx)) >>>> + return 0; >>>> + >>>> + /* >>>> + * We don't expect to ever hit this. If ever required, we would have >>>> + * to duplicate the tracking. >>>> + */ >>>> + if (unlikely(kref_read(&ctx->kref) >= REFCOUNT_MAX)) >>> >>> How not expected is this? :) maybe use WARN_ON_ONCE() if it really should >>> never happen? >> I guess if we mmap a large PFNMAP and then split it into individual >> PTE-sized chunks, we could get many VMAs per-process referencing that >> tracing. >> >> Combine that with fork() and I assume one could hit this -- when really >> trying hard to achieve it. (probably as privileged user to get a big >> VM_PFNMAP, though, but not sure) > > Right ok, yeah I guess so. It'd be good to see if we could trigger it somehow :) > >> >> In that case, a WARN_ON_ONCE() would be bad -- because it could be triggered >> by the user. > > Ack > >> >> We could do a pr_warn_once() instead, stating that this is not supported >> right now? > > Hmm, if we truly think it might happen let's avoid printing anything for now. > > Maybe just ++todo for experimenting with triggering? > > It's not hugely important! Agreed. I assume it's similar to our mapcount vs. refcount overflows. if you really want to trigger it, there might be some weird way .. but it's no longer in the "valid use case" area :) -- Cheers, David / dhildenb