On Mon, Nov 05, 2018 at 06:04:42PM +0000, Nadav Amit wrote: > 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?
Sure; but all of x86_32 relies on kmap_atomic. This was just the the one way I ran into it again. By our current way of thinking, kmap_atomic simply is not correct.
