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Peter Anvin" , Mike Rapoport , Lorenzo Stoakes , Toshi Kani , linux-mm@kvack.org, regressions@lists.linux.dev, linux-kernel@vger.kernel.org References: <20260916062222.27347-1-mikhail.v.gavrilov@gmail.com> From: Dave Hansen Content-Language: en-US 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: This is a multi-part message in MIME format. --------------8ltgeDxBJN0BN2U8yZ01aJMF Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/23/26 11:38, Pedro Falcato wrote: > So, the question is: why the heck do we need a copy? PMD is still allocated > by the time we flush the TLB. Why doesn't a simple pud_clear() + flush_tlb + > free over the pmd Just Work? Am I missing something? The git log isn't > clueing me in. Yeah, the original changelog in here: commit 5e0fb5df2ee871b841f96f9cb6a7f2784e96aa4e Author: Toshi Kani Date: Wed Jun 27 08:13:48 2018 -0600 x86/mm: Add TLB purge to free pmd/pte page interfaces is a bit vague about what it is doing. I think there might have been some confusion around speculation: speculation may cache pud/pmd entries (paging-structure caches) when they have P-bit set Because, as far as I know, you can't have establish an entry in the TLB, period, if Accessed==0. I think the changelog imagines a world where the CPU is establishing TLB entries from Present=1,Accessed=0 PTEs. That just doesn't happen. There are only two ways the CPU can find a page table entry to cache in the TLB and start setting Accessed bits: 1. It walks down from CR3 and finds the entry 2. It starts from a mid-level cache and finds the entry This takes care of a walk from CR3 (#1): pud_clear(pud); and this takes care of the mid-level caches (#2): /* INVLPG to clear all paging-structure caches */ flush_tlb_kernel_range(addr, addr + PAGE_SIZE-1); I don't think there's anything else to do. Right? I think that means we can do something like the completely untested attached patch. Looks like Mikhail came to basically the same conclusion. --------------8ltgeDxBJN0BN2U8yZ01aJMF Content-Type: text/x-patch; charset=UTF-8; name="pud_free_pmd_page-simplify.patch" Content-Disposition: attachment; filename="pud_free_pmd_page-simplify.patch" Content-Transfer-Encoding: base64 CgotLS0KCiBiL2FyY2gveDg2L21tL3BndGFibGUuYyB8ICAgMzAgKysrKysrKysrKy0tLS0t LS0tLS0tLS0tLS0tLS0tCiAxIGZpbGUgY2hhbmdlZCwgMTAgaW5zZXJ0aW9ucygrKSwgMjAg ZGVsZXRpb25zKC0pCgpkaWZmIC1wdU4gYXJjaC94ODYvbW0vcGd0YWJsZS5jfnB1ZF9mcmVl X3BtZF9wYWdlLXNpbXBsaWZ5IGFyY2gveDg2L21tL3BndGFibGUuYwotLS0gYS9hcmNoL3g4 Ni9tbS9wZ3RhYmxlLmN+cHVkX2ZyZWVfcG1kX3BhZ2Utc2ltcGxpZnkJMjAyNi0wOS0yMyAx NTozMDozMi4wMzU2MTA0NzUgLTA3MDAKKysrIGIvYXJjaC94ODYvbW0vcGd0YWJsZS5jCTIw MjYtMDktMjMgMTU6MzY6NTYuNjYzNzQ3NTg2IC0wNzAwCkBAIC0xLDQgKzEsNCBAQAotLy8g U1BEWC1MaWNlbnNlLUlkZW50aWZpZXI6IEdQTC0yLjAKK3B1ZF9mcmVlX3BtZF9wYWdlLXNp bXBsaWZ5Ly8gU1BEWC1MaWNlbnNlLUlkZW50aWZpZXI6IEdQTC0yLjAKICNpbmNsdWRlIDxs aW51eC9tbS5oPgogI2luY2x1ZGUgPGxpbnV4L2dmcC5oPgogI2luY2x1ZGUgPGxpbnV4L2h1 Z2V0bGIuaD4KQEAgLTcxMSw0NCArNzExLDM0IEBAIGludCBwbWRfY2xlYXJfaHVnZShwbWRf dCAqcG1kKQogICogQGFkZHI6IFZpcnR1YWwgYWRkcmVzcyBhc3NvY2lhdGVkIHdpdGggUFVE CiAgKgogICogQ29udGV4dDogVGhlIFBVRCByYW5nZSBoYXMgYmVlbiB1bm1hcHBlZCBhbmQg VExCIHB1cmdlZC4KLSAqIFJldHVybjogMSBpZiBjbGVhcmluZyB0aGUgZW50cnkgc3VjY2Vl ZGVkLiAwIG90aGVyd2lzZS4KICAqCiAgKiBOT1RFOiBDYWxsZXJzIG11c3QgYWxsb3cgYSBz aW5nbGUgcGFnZSBhbGxvY2F0aW9uLgogICovCi1pbnQgcHVkX2ZyZWVfcG1kX3BhZ2UocHVk X3QgKnB1ZCwgdW5zaWduZWQgbG9uZyBhZGRyKQordm9pZCBwdWRfZnJlZV9wbWRfcGFnZShw dWRfdCAqcHVkLCB1bnNpZ25lZCBsb25nIGFkZHIpCiB7Ci0JcG1kX3QgKnBtZCwgKnBtZF9z djsKIAlzdHJ1Y3QgcHRkZXNjICpwdDsKKwlwbWRfdCAqcG1kOwogCWludCBpOwogCiAJcG1k ID0gcHVkX3BndGFibGUoKnB1ZCk7Ci0JcG1kX3N2ID0gKHBtZF90ICopX19nZXRfZnJlZV9w YWdlKEdGUF9LRVJORUwpOwotCWlmICghcG1kX3N2KQotCQlyZXR1cm4gMDsKLQotCWZvciAo aSA9IDA7IGkgPCBQVFJTX1BFUl9QTUQ7IGkrKykgewotCQlwbWRfc3ZbaV0gPSBwbWRbaV07 Ci0JCWlmICghcG1kX25vbmUocG1kW2ldKSkKLQkJCXBtZF9jbGVhcigmcG1kW2ldKTsKLQl9 CiAKIAlwdWRfY2xlYXIocHVkKTsKIAotCS8qIElOVkxQRyB0byBjbGVhciBhbGwgcGFnaW5n LXN0cnVjdHVyZSBjYWNoZXMgKi8KKwkvKgorCSAqICdwbWQnIGFuZCBhbGwgaXRzIGRlc2Nl bmRlbnRzIGFyZSB1bnJlYWNoYWJsZQorCSAqIHZpYSBub3JtYWwgcGFnZSB3YWxrcy4gTWFr ZSB0aGVtIHVucmVhY2hhYmxlCisJICogaW4gY2FjaGVkIG1pZC1sZXZlbCB3YWxrcyB0b286 CisJICovCiAJZmx1c2hfdGxiX2tlcm5lbF9yYW5nZShhZGRyLCBhZGRyICsgUEFHRV9TSVpF LTEpOwogCiAJZm9yIChpID0gMDsgaSA8IFBUUlNfUEVSX1BNRDsgaSsrKSB7Ci0JCWlmICgh cG1kX25vbmUocG1kX3N2W2ldKSkgewotCQkJcHQgPSBwYWdlX3B0ZGVzYyhwbWRfcGFnZShw bWRfc3ZbaV0pKTsKKwkJaWYgKCFwbWRfbm9uZShwbWRbaV0pKSB7CisJCQlwdCA9IHBhZ2Vf cHRkZXNjKHBtZF9wYWdlKHBtZFtpXSkpOwogCQkJcGFnZXRhYmxlX2R0b3JfZnJlZShwdCk7 CiAJCX0KIAl9CiAKLQlmcmVlX3BhZ2UoKHVuc2lnbmVkIGxvbmcpcG1kX3N2KTsKLQogCXBt ZF9mcmVlKCZpbml0X21tLCBwbWQpOwotCi0JcmV0dXJuIDE7CiB9CiAKIC8qKgpfCg== --------------8ltgeDxBJN0BN2U8yZ01aJMF--