Messages in this thread | | | Date | Mon, 14 May 2018 17:41:37 -0700 | From | Matthew Wilcox <> | Subject | Re: [PATCH] mm: Add new vma flag VM_LOCAL_CPU |
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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.
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