Messages in this thread | | | Date | Thu, 24 Aug 2017 12:49:36 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH v2] x86: enable RCU based table free |
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On Thu, Aug 24, 2017 at 11:22:58AM +0200, Vitaly Kuznetsov wrote: > On x86 software page-table walkers depend on the fact that remote TLB flush > does an IPI: walk is performed lockless but with interrupts disabled and in > case the pagetable is freed the freeing CPU will get blocked as remote TLB > flush is required. On other architecture which don't require an IPI to do > remote TLB flush we have an RCU-based mechanism (see > include/asm-generic/tlb.h for more details). > > In virtualized environments we may want to override .flush_tlb_others hook > in pv_mmu_ops and use a hypercall asking the hypervisor to do remote TLB > flush for us. This breaks the assumption about IPI. Xen PV does this for > years and the upcoming remote TLB flush for Hyper-V will do it too. This > is not safe, software pagetable walkers may step on an already freed page. > > Solve the issue by enabling RCU-based table free mechanism. Testing with > kernbench and mmap/munmap microbenchmars didn't show any notable > performance impact. > > Suggested-by: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> > Acked-by: Juergen Gross <jgross@suse.com> > --- > Changes since v1: > - Enable HAVE_RCU_TABLE_FREE unconditionally to avoid different code pathes > for no reason [Linus Torvalds]
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
-- Kirill A. Shutemov
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