On Mon, May 14, 2018 at 10:37:38PM +0300, Boaz Harrosh wrote: > On 14/05/18 22:15, Matthew Wilcox wrote: > > On Mon, May 14, 2018 at 08:28:01PM +0300, Boaz Harrosh wrote: > >> On a call to mmap an mmap provider (like an FS) can put > >> this flag on vma->vm_flags. > >> > >> The VM_LOCAL_CPU flag tells the Kernel that the vma will be used > >> from a single-core only, and therefore invalidation (flush_tlb) of > >> PTE(s) need not be a wide CPU scheduling. > > > > I still don't get this. You're opening the kernel up to being exploited > > by any application which can persuade it to set this flag on a VMA. > > > > No No this is not an application accessible flag this can only be set > by the mmap implementor at ->mmap() time (Say same as VM_VM_MIXEDMAP). > > Please see the zuf patches for usage (Again apologise for pushing before > a user) > > The mmap provider has all the facilities to know that this can not be > abused, not even by a trusted Server. I don't think page tables work the way you think they work. + err = vm_insert_pfn_prot(zt->vma, zt_addr, pfn, prot); That doesn't just insert it into the local CPU's page table. Any CPU which directly accesses or even prefetches that address will also get the translation into its cache.
