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Peter Anvin" , "Mike Rapoport (Microsoft)" , Kiryl Shutsemau Cc: Andrew Morton , David Carlier , Vlastimil Babka , David Hildenbrand , "Liam R. Howlett" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, stable@vger.kernel.org References: <20260710-fix-cpa-ptdump-race-v1-1-d898699a7417@kernel.org> Content-Language: en-US From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzUVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT7CwXgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lczsFNBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABwsFfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y In-Reply-To: <20260710-fix-cpa-ptdump-race-v1-1-d898699a7417@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: C68301C0003 X-Stat-Signature: e95nj9a9xb9komto8cz8digqz1ipbiqb X-HE-Tag: 1783700810-286927 X-HE-Meta: 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 Vjdbj3uB tOebLwjmh3ePPSXKN1dh+hQSTbnpH9pT+tqSPdj7sqIhCWlzgNK6Sa4WrSfzY2WIW5hz4YHxstr4aPkg3Ir7xvrqmGqBIXtadVumnNWlCSCiT1h7E0zbgsf6OKymQCkwskhVdMGdXcylqyeHgyOILWhLW8BdohoBJAlVUYy7/FbO+6KMmtDNvlLGiJbJdUdpAIvRQVmxa6UqbpXc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/10/26 04:56, Lorenzo Stoakes wrote: > This patch resolves the issue by acquiring the mmap read lock on init_mm to > provide mutual exclusion against ptdump, which acquires the init_mm write > lock. Hey Lorenzo, Thanks for looking at this! This isn't wrong per-se. ptdump does _sometimes_ acquire the init_mm write lock. But the fun comes when ptdump_curknl_show() passes current->mm in to the ptdump code. In that case, there's no init_mm locking. I think the 'efi_mm' code has the same issue since it shares some of the kernel page tables. Is that your read on it too? In the end, I think the issue is that there's not even *a* correct mmap lock to take. The userspace half of the address space needs the current->mm mmap lock and the kernel half needs the init_mm mmap lock. The naming here doesn't help because the "current_kernel" file doesn't dump the current kernel page tables, it dumps the whole kernel *copy* (the only copy with PTI off) which includes userspace. (Note: maybe we should hide "current_user" when PTI is off at runtime) So what do we do? 1. We could just bite the bullet and have separate ptdump files for the top and bottom of the address space: current_kernel_top current_kernel_bottom current_user_top current_user_bottom etc.. Then the lock you take is dictated by the file. 2. We could always take both init_mm and current->mm locks. That seems icky. 3. We could have ptdump_walk_pgd() take a different lock for each 'range'. Logically: if (range->start < PAGE_OFFSET) mmap_write_lock(mm); else mmap_write_lock(&init_mm); That's icky too and it means a range can't cross PAGE_OFFSET, but that doesn't seem too bad (it could also WARN() if it sees bad ranges). 4. We do something fancier with the free like RCU (I think this may have been discussed already). I'm kinda leaning toward #3.