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[109.42.51.26]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-430ccf5181fsm72311515e9.25.2024.10.11.04.39.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Oct 2024 04:39:25 -0700 (PDT) Message-ID: <33c40562-fd22-4517-9f56-1039289a55e5@redhat.com> Date: Fri, 11 Oct 2024 13:39:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 0/2] mm: don't install PMD mappings when THPs are disabled by the hw/process/vma To: David Hildenbrand , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, kvm@vger.kernel.org, Andrew Morton , Hugh Dickins , "Matthew Wilcox (Oracle)" , Ryan Roberts , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Kefeng Wang References: <20241011102445.934409-1-david@redhat.com> From: Thomas Huth Autocrypt: addr=thuth@redhat.com; keydata= xsFNBFH7eUwBEACzyOXKU+5Pcs6wNpKzrlJwzRl3VGZt95VCdb+FgoU9g11m7FWcOafrVRwU yYkTm9+7zBUc0sW5AuPGR/dp3pSLX/yFWsA/UB4nJsHqgDvDU7BImSeiTrnpMOTXb7Arw2a2 4CflIyFqjCpfDM4MuTmzTjXq4Uov1giGE9X6viNo1pxyEpd7PanlKNnf4PqEQp06X4IgUacW tSGj6Gcns1bCuHV8OPWLkf4hkRnu8hdL6i60Yxz4E6TqlrpxsfYwLXgEeswPHOA6Mn4Cso9O 0lewVYfFfsmokfAVMKWzOl1Sr0KGI5T9CpmRfAiSHpthhHWnECcJFwl72NTi6kUcUzG4se81 O6n9d/kTj7pzTmBdfwuOZ0YUSqcqs0W+l1NcASSYZQaDoD3/SLk+nqVeCBB4OnYOGhgmIHNW 0CwMRO/GK+20alxzk//V9GmIM2ACElbfF8+Uug3pqiHkVnKqM7W9/S1NH2qmxB6zMiJUHlTH gnVeZX0dgH27mzstcF786uPcdEqS0KJuxh2kk5IvUSL3Qn3ZgmgdxBMyCPciD/1cb7/Ahazr 3ThHQXSHXkH/aDXdfLsKVuwDzHLVSkdSnZdt5HHh75/NFHxwaTlydgfHmFFwodK8y/TjyiGZ zg2Kje38xnz8zKn9iesFBCcONXS7txENTzX0z80WKBhK+XSFJwARAQABzR5UaG9tYXMgSHV0 aCA8dGh1dGhAcmVkaGF0LmNvbT7CwXgEEwECACIFAlVgX6oCGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAAoJEC7Z13T+cC21EbIP/ii9cvT2HHGbFRl8HqGT6+7Wkb+XLMqJBMAIGiQK QIP3xk1HPTsLfVG0ao4hy/oYkGNOP8+ubLnZen6Yq3zAFiMhQ44lvgigDYJo3Ve59gfe99KX EbtB+X95ODARkq0McR6OAsPNJ7gpEUzfkQUUJTXRDQXfG/FX303Gvk+YU0spm2tsIKPl6AmV 1CegDljzjycyfJbk418MQmMu2T82kjrkEofUO2a24ed3VGC0/Uz//XCR2ZTo+vBoBUQl41BD eFFtoCSrzo3yPFS+w5fkH9NT8ChdpSlbNS32NhYQhJtr9zjWyFRf0Zk+T/1P7ECn6gTEkp5k ofFIA4MFBc/fXbaDRtBmPB0N9pqTFApIUI4vuFPPO0JDrII9dLwZ6lO9EKiwuVlvr1wwzsgq zJTPBU3qHaUO4d/8G+gD7AL/6T4zi8Jo/GmjBsnYaTzbm94lf0CjXjsOX3seMhaE6WAZOQQG tZHAO1kAPWpaxne+wtgMKthyPLNwelLf+xzGvrIKvLX6QuLoWMnWldu22z2ICVnLQChlR9d6 WW8QFEpo/FK7omuS8KvvopFcOOdlbFMM8Y/8vBgVMSsK6fsYUhruny/PahprPbYGiNIhKqz7 UvgyZVl4pBFjTaz/SbimTk210vIlkDyy1WuS8Zsn0htv4+jQPgo9rqFE4mipJjy/iboDzsFN BFH7eUwBEAC2nzfUeeI8dv0C4qrfCPze6NkryUflEut9WwHhfXCLjtvCjnoGqFelH/PE9NF4 4VPSCdvD1SSmFVzu6T9qWdcwMSaC+e7G/z0/AhBfqTeosAF5XvKQlAb9ZPkdDr7YN0a1XDfa +NgA+JZB4ROyBZFFAwNHT+HCnyzy0v9Sh3BgJJwfpXHH2l3LfncvV8rgFv0bvdr70U+On2XH 5bApOyW1WpIG5KPJlDdzcQTyptOJ1dnEHfwnABEfzI3dNf63rlxsGouX/NFRRRNqkdClQR3K gCwciaXfZ7ir7fF0u1N2UuLsWA8Ei1JrNypk+MRxhbvdQC4tyZCZ8mVDk+QOK6pyK2f4rMf/ WmqxNTtAVmNuZIwnJdjRMMSs4W4w6N/bRvpqtykSqx7VXcgqtv6eqoDZrNuhGbekQA0sAnCJ VPArerAZGArm63o39me/bRUQeQVSxEBmg66yshF9HkcUPGVeC4B0TPwz+HFcVhheo6hoJjLq knFOPLRj+0h+ZL+D0GenyqD3CyuyeTT5dGcNU9qT74bdSr20k/CklvI7S9yoQje8BeQAHtdV cvO8XCLrpGuw9SgOS7OP5oI26a0548M4KldAY+kqX6XVphEw3/6U1KTf7WxW5zYLTtadjISB X9xsRWSU+Yqs3C7oN5TIPSoj9tXMoxZkCIHWvnqGwZ7JhwARAQABwsFfBBgBAgAJBQJR+3lM AhsMAAoJEC7Z13T+cC21hPAQAIsBL9MdGpdEpvXs9CYrBkd6tS9mbaSWj6XBDfA1AEdQkBOn ZH1Qt7HJesk+qNSnLv6+jP4VwqK5AFMrKJ6IjE7jqgzGxtcZnvSjeDGPF1h2CKZQPpTw890k fy18AvgFHkVk2Oylyexw3aOBsXg6ukN44vIFqPoc+YSU0+0QIdYJp/XFsgWxnFIMYwDpxSHS 5fdDxUjsk3UBHZx+IhFjs2siVZi5wnHIqM7eK9abr2cK2weInTBwXwqVWjsXZ4tq5+jQrwDK cvxIcwXdUTLGxc4/Z/VRH1PZSvfQxdxMGmNTGaXVNfdFZjm4fz0mz+OUi6AHC4CZpwnsliGV ODqwX8Y1zic9viSTbKS01ZNp175POyWViUk9qisPZB7ypfSIVSEULrL347qY/hm9ahhqmn17 Ng255syASv3ehvX7iwWDfzXbA0/TVaqwa1YIkec+/8miicV0zMP9siRcYQkyTqSzaTFBBmqD oiT+z+/E59qj/EKfyce3sbC9XLjXv3mHMrq1tKX4G7IJGnS989E/fg6crv6NHae9Ckm7+lSs IQu4bBP2GxiRQ+NV3iV/KU3ebMRzqIC//DCOxzQNFNJAKldPe/bKZMCxEqtVoRkuJtNdp/5a yXFZ6TfE1hGKrDBYAm4vrnZ4CXFSBDllL59cFFOJCkn4Xboj/aVxxJxF30bn In-Reply-To: <20241011102445.934409-1-david@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 22E151C001A X-Stat-Signature: uy1hsxwukhn5e4n936haq84t7oc699p6 X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1728646766-590867 X-HE-Meta: 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 dsM1AHKZ nRf6RoDdOjVlLHmZeGr6rQe8VKZMxlJT4CFv+h1Y3hovbdMsBq3CJjykLwj+DtG9vpwsrYFx+3+zLhV/00qQACoASJF5+W7FOHsls7r6jqwOASzAadmJuLphOlREiGzsZeRZOTJhgcHpnUPI8orGQ0/nAfZ0oNKHY0sRSeF7Ry3hVQWk9yZpmWgBhz1GyP3SimTOpDLPia+ThKUTqX0rBCSPARhPA27iP2rCNcUwrg9PEX8srPlf/cn4+8Rk+krG1fLzTegG+eOr/iHHQgGDWx3M9uGObb2lJbdWMqPXGoZWJNJeStQwiOlqOZb6V+rSbEkKSeZ30EojSqJmuXwOwmHQdajXT6WS/ARXudAoO+N5tr3XCLC6Wg34u4YLSjAs9bmnD0jhqKJ2DK4/Dom5aDgrX1Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/10/2024 12.24, David Hildenbrand wrote: > During testing, it was found that we can get PMD mappings in processes > where THP (and more precisely, PMD mappings) are supposed to be disabled. > While it works as expected for anon+shmem, the pagecache is the problematic > bit. > > For s390 KVM this currently means that a VM backed by a file located on > filesystem with large folio support can crash when KVM tries accessing > the problematic page, because the readahead logic might decide to use > a PMD-sized THP and faulting it into the page tables will install a > PMD mapping, something that s390 KVM cannot tolerate. > > This might also be a problem with HW that does not support PMD mappings, > but I did not try reproducing it. > > Fix it by respecting the ways to disable THPs when deciding whether we > can install a PMD mapping. khugepaged should already be taking care of > not collapsing if THPs are effectively disabled for the hw/process/vma. > > An earlier patch was tested by Thomas Huth, this one still needs to > be retested; sending it out already. I just finished testing your new version of these patches here, and I can confirm that they are fixing the problem that I was facing, so: Tested-by: Thomas Huth FWIW, the problem can be reproduced by running a KVM guest on a s390x host like this: qemu-system-s390x -accel kvm -nographic -m 4G -d guest_errors \ -M s390-ccw-virtio,memory-backend=mem-machine_mem \ -object memory-backend-file,size=4294967296,prealloc=true,mem-path=$HOME/myfile,share=true,id=mem-machine_mem Without the fix, the guest crashes immediatly before being able to execute the first instruction. With the fix applied, you can still see the first messages of the guest firmware, indicating that the guest started successfully. Thank you very much for the fix, David! Thomas