From: Peter Zijlstra Sent: November 5, 2018 at 1:30:41 PM GMT > To: Nadav Amit <[email protected]> > Cc: Ingo Molnar <[email protected]>, [email protected], > [email protected], H. Peter Anvin <[email protected]>, Thomas Gleixner > <[email protected]>, Borislav Petkov <[email protected]>, Dave Hansen > <[email protected]>, Andy Lutomirski <[email protected]>, Kees Cook > <[email protected]>, Dave Hansen <[email protected]>, Masami > Hiramatsu <[email protected]> > Subject: Re: [PATCH v3 6/7] x86/alternatives: use temporary mm for text poking > > > On Fri, Nov 02, 2018 at 04:29:45PM -0700, Nadav Amit wrote: >> + unuse_temporary_mm(prev); >> + >> + pte_unmap_unlock(ptep, ptl); > > That; that does kunmap_atomic() on 32bit. > > I've been thinking that the whole kmap_atomic thing on x86_32 is > terminally broken, and with that most of x86_32 is. > > kmap_atomic does the per-cpu fixmap pte fun-and-games we're here saying > is broken. Yes, only the one CPU will (explicitly) use those fixmap PTEs > and thus the local invalidate _should_ work. However nothing prohibits > speculation on another CPU from using our fixmap addresses. Which can > lead to the remote CPU populating its TLBs for our fixmap entry. > > And, as we've found, there are AMD parts that #MC when there are > mis-matched TLB entries. > > So what do we do? mark x86_32 SMP broken?
pte_unmap() seems to only use kunmap_atomic() when CONFIG_HIGHPTE is set, no? Do most distributions run with CONFIG_HIGHPTE?
