On Wed, Aug 29, 2018 at 2:28 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Wed, Aug 29, 2018 at 01:11:46AM -0700, Nadav Amit wrote: >> + pte_clear(poking_mm, poking_addr, ptep); >> + >> + /* >> + * __flush_tlb_one_user() performs a redundant TLB flush when PTI is on, >> + * as it also flushes the corresponding "user" address spaces, which >> + * does not exist. >> + * >> + * Poking, however, is already very inefficient since it does not try to >> + * batch updates, so we ignore this problem for the time being. >> + * >> + * Since the PTEs do not exist in other kernel address-spaces, we do >> + * not use __flush_tlb_one_kernel(), which when PTI is on would cause >> + * more unwarranted TLB flushes. >> + */ > > yuck :-), but yeah. I'm sure we covered this ad nauseum when PTI was being developed, but we were kind of in a rush, so: Why do we do INVPCID at all? The fallback path for non-INVPCID systems uses invalidate_user_asid(), which should be faster than the invpcid path. And doesn't do a redundant flush in this case. Can we just drop the INVPCID? While we're at it, we could drop X86_FEATURE_INVPCID_SINGLE entirely, since that's the only user. --Andy
