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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: CCD001C0025 X-Stat-Signature: 3toehpkaxsjudyhghxxzubzyxctpamb1 X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1728316714-852794 X-HE-Meta: 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 Mxo7VMG2 wgB9CuKZfOuGbjXAi1iJpbZJ/0rglewxqC4bLyUGQMzA31h9Waff5LbuR1Chl/fh9V+bf6MhGtr9699NCEv9+ZcBFlfOyi9BmrNF3ESQ5r5DTW9QXvWoDvrNsIfxlShZSjpUpq1TEM9U8jVXr7c/AxTG1T3TdvM98yFdnZEpix8NZkrY1yA9tp3OozZAf3RMLDBt6EaP8UnpMgpk759zBRw6kA7+02lUsPJ//0ertfMWO60g= 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 10/7/24 01:44, David Hildenbrand wrote: > On 02.10.24 19:35, Dave Hansen wrote: >> We were just chatting about this on David Rientjes's MM alignment call. > > Unfortunately I was not able to attend this time, my body decided it's a > good idea to stay in bed for a couple of days. > >> I thought I'd try to give a little brain >> >> Let's start by thinking about KVM and secondary MMUs.  KVM has a primary >> mm: the QEMU (or whatever) process mm.  The virtualization (EPT/NPT) >> tables get entries that effectively mirror the primary mm page tables >> and constitute a secondary MMU.  If the primary page tables change, >> mmu_notifiers ensure that the changes get reflected into the >> virtualization tables and also that the virtualization paging structure >> caches are flushed. >> >> msharefs is doing something very similar.  But, in the msharefs case, >> the secondary MMUs are actually normal CPU MMUs.  The page tables are >> normal old page tables and the caches are the normal old TLB.  That's >> what makes it so confusing: we have lots of infrastructure for dealing >> with that "stuff" (CPU page tables and TLB), but msharefs has >> short-circuited the infrastructure and it doesn't work any more. > > It's quite different IMHO, to a degree that I believe they are different > beasts: > > Secondary MMUs: > * "Belongs" to same MM context and the primary MMU (process page tables) I think you're speaking to the ratio here. For each secondary MMU, I think you're saying that there's one and only one mm_struct. Is that right? > * Maintains separate tables/PTEs, in completely separate page table >   hierarchy This is the case for KVM and the VMX/SVM MMUs, but it's not generally true about hardware. IOMMUs can walk x86 page tables and populate the IOTLB from the _same_ page table hierarchy as the CPU.