Hi Punit, Thank you for having a look! On 9/11/20 9:34 AM, Punit Agrawal wrote: > Hi Alexandru, > > Alexandru Elisei <alexandru.elisei@xxxxxxx> writes: > >> When userspace uses hugetlbfs for the VM memory, user_mem_abort() tries to >> use the same block size to map the faulting IPA in stage 2. If stage 2 >> cannot the same block mapping because the block size doesn't fit in the >> memslot or the memslot is not properly aligned, user_mem_abort() will fall >> back to a page mapping, regardless of the block size. We can do better for >> PUD backed hugetlbfs by checking if a PMD block mapping is supported before >> deciding to use a page. > I think this was discussed in the past. > > I have a vague recollection of there being a problem if the user and > stage 2 mappings go out of sync - can't recall the exact details. I'm not sure what you mean by the two tables going out of sync. I'm looking at Documentation/vm/unevictable-lru.rst and this is what it says regarding hugetlbfs: "VMAs mapping hugetlbfs page are already effectively pinned into memory. We neither need nor want to mlock() these pages. However, to preserve the prior behavior of mlock() - before the unevictable/mlock changes - mlock_fixup() will call make_pages_present() in the hugetlbfs VMA range to allocate the huge pages and populate the ptes." Please correct me if I'm wrong, but my interpretation is that once a hugetlbfs page has been mapped in a process' address space, the only way to unmap it is via munmap. If that's the case, the KVM mmu notifier should take care of unmapping from stage 2 the entire memory range addressed by the hugetlbfs pages, right? > > Putting it out there in case anybody else on the thread can recall the > details of the previous discussion (offlist). > > Though things may have changed and if it passes testing - then maybe I > am mis-remembering. I'll take a closer look at the patch and shout out > if I notice anything. The test I ran was to boot a VM and run ltp (with printk's sprinkled in the host kernel to see what page size and where it gets mapped/unmapped at stage 2). Do you mind recommending other tests that I might run? Thanks, Alex _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
