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U2FsdGVkX180ktL4jVY+XT/MUd+f+dduejwrz0ySk9MfPlSF9FImAuuZfg3Xw7MkRA8llcfrDtzJgxP3nrTR82g9cwy6s5RFr/7QMiHHAgyw4thqo3hb+4fr67OwKCvFlT7RbszAE7TvI5oz5X5qdp0hNWGd0/GUXsGin6R1rn1cnviZ1vdvmcRDguhAQIQ44qmu6sYAhS8wm7A8Y3zxZxCuAVycMI1gAbjJLYiTsIM0WwSGaWIveRgBDLqnUvsErcDpGzPemJWoAppq5+mTR5WZ/BDgHwcSJzXreyAxMfoPSxTC2s/1BnFcF49w45Wqah3SMlLRMAykO/Ga+lTTFXFkkwHg6P1jdar04O8fvg5vFMK5DdSIGxIIJfIesCiyrI3G3CZsbAzMZheQrfS/Wwq33VLnTzSLjRwLHhpaS93gcdyyUBULRbOXGaMQhMHVXqEqco4tCekle1jf4qlOis7zEDloMogX5AXIqFsYieGx1a9vzO78EbWvp8M1Yo2CWRefSPhSQpnY/wrGECM4rcae7feqBGUj0W4D9RnHlU5lrhXoZmGEzqBMVCRjOY6r/cxJHL7cELAJTaZb7Hrit7rsxZxYOZEU7pIfBT2fF4OTlk9GxDqnOlVRD2GGj6lG4lMS8FDXLdbffnR9/ZxqtopuhvUZS+sG9veX/MGT1HyuUbf7rZuY8TZPnJO7JhvevvxkSaUEQ5EjoIyhgWG/HnsV+UmINUrnb8H9YVmpoGW1r4JqP9CjGku6PIH4/MUZgrXrwc67ZuEo0BX9h+I9eOY6y233DpAF8w2GIn01bkaGE3kiL5OR04uOEy3W4gNnrb6bR4h9YAVbGcI59XkhVwdl/ouegdR/PdsbvBCulfjYho9GDQKcupFlgWUcCxrlQc5yuuZUZH+vV9q7sJeGZg95X8Iadym5/pqg5OoKim7scY1PZpmbK1ZDBCo+GzNe/WHOa36t5pgrWOZsNPr ExO+ifT6 dWL2vleuZtF7FC2lN1oFZC3H5+6JSVf39Zs3edXPcELH/p94/OyignuvqQNcb9y8kd1y5g6EABju6COL0gP5/ZRCOUEpW1eS4rP3JY3+ZJdjVEf2q1Kx1LyoB8xBnyLtPqBY41f4IKdgAXq7gyufwQjxeK6wUYDo0fIieW1/ydibLXHQAV+OcyCHsy7vxCXI3s8ovgralDjtyq4QozgDpsw2qch3e4yVqSc/JEe334N5GOV2VhNj5PfNgBrM96DR/hVXyyrTNrUfVT5ZHhiKzSG6YAgugBHUmTTIhIo3yGTz6iDP6G+W9o3alESpKyPOcivOzUYimsy1Os2LE32usTk4dbkQQgx+v/BdGFIdH1Iloaid2zGKmmNpPa1u1xyaxJIZQUwHhfY9v70aP2Jd3G/WvMdSlR0kn33C6BC9VNQLjFSZwgDlA22QTfcPB0zPfOI0eNbh9w9YRUv+ZakGkwoF/jjm3f0dnNQUzrZCIzMOfZCCMZPmcmCohbhO5gW10/7/cUYbADm0NUV1pTTu3+cSt8UUqTshxo45uS1cttFWwKm91i9xDBoUS7OBlhIsVw0RnxhzNFHOyCZzonl4jSWQzrcdBfUlibbn2o+UHlYEjGHf1J94SxlmIIMxuUu92VQHt 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 10/14/24 1:07 PM, Jann Horn wrote: > On Wed, Sep 4, 2024 at 1:22 AM Anthony Yznaga wrote: >> One major issue to address for this series to function correctly >> is how to ensure proper TLB flushing when a page in a shared >> region is unmapped. For example, since the rmaps for pages in a >> shared region map back to host vmas which point to a host mm, TLB >> flushes won't be directed to the CPUs the sharing processes have >> run on. I am by no means an expert in this area. One idea is to >> install a mmu_notifier on the host mm that can gather the necessary >> data and do flushes similar to the batch flushing. > The mmu_notifier API has two ways you can use it: > > First, there is the classic mode, where before you start modifying > PTEs in some range, you remove mirrored PTEs from some other context, > and until you're done with your PTE modification, you don't allow > creation of new mirrored PTEs. This is intended for cases where > individual PTE entries are copied over to some other context (such as > EPT tables for virtualization). When I last looked at that code, it > looked fine, and this is what KVM uses. But it probably doesn't match > your usecase, since you wouldn't want removal of a single page to > cause the entire page table containing it to be temporarily unmapped > from the processes that use it? No, definitely don't want to do that. :-) > > Second, there is a newer mode for IOMMUv2 stuff (using the > mmu_notifier_ops::invalidate_range callback), where the idea is that > you have secondary MMUs that share the normal page tables, and so you > basically send them invalidations at the same time you invalidate the > primary MMU for the process. I think that's the right fit for this > usecase; however, last I looked, this code was extremely broken (see > https://lore.kernel.org/lkml/CAG48ez2NQKVbv=yG_fq_jtZjf8Q=+Wy54FxcFrK_OujFg5BwSQ@mail.gmail.com/ > for context). Unless that's changed in the meantime, I think someone > would have to fix that code before it can be relied on for new > usecases. Thank you for this background! Looks like there have since been some changes to the mmu notifiers, and the invalidate_range callback became arch_invalidate_secondary_tlbs. I'm currently looking into using it to flush all TLBs. Anthony