On Mon, Dec 4, 2017 at 2:47 PM, Peter Zijlstra <pet...@infradead.org> wrote: > On Mon, Dec 04, 2017 at 02:22:54PM -0800, Andy Lutomirski wrote: > >> > +static inline void invalidate_pcid_other(void) >> > +{ >> > + /* >> > + * With global pages, all of the shared kenel page tables >> > + * are set as _PAGE_GLOBAL. We have no shared nonglobals >> > + * and nothing to do here. >> > + */ >> > + if (!static_cpu_has_bug(X86_BUG_CPU_SECURE_MODE_KPTI)) >> > + return; >> >> I think I'd be more comfortable if this check were in the caller, not >> here. Shouldn't a function called invalidate_pcid_other() do what the >> name says? > > Yeah, you're probably right. The thing is course that we only ever need > that operation for kpti (as of now). But me renaming this stuff made > this problem :/ > >> > + this_cpu_write(cpu_tlbstate.invalidate_other, true); >> >> Why do we need this extra variable instead of just looping over all >> other ASIDs and invalidating them? It would be something like: >> >> for (i = 1; i < TLB_NR_DYN_ASIDS; i++) { >> if (i != this_cpu_read(cpu_tlbstate.loaded_mm_asid)) >> this_cpu_write(cpu_tlbstate.ctxs[i].ctx_id, 0); >> } >> >> modulo epic whitespace damage and possible typos. > > I think the point is that we can do many invalidate_other's before we > ever do a switch_mm(). The above would be more expensive. > > Not sure it would matter in practise though. > >> > static inline void __flush_tlb_one(unsigned long addr) >> > { >> > count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ONE); >> > __flush_tlb_single(addr); >> > + /* >> > + * Invalidate other address spaces inaccessible to single-page >> > + * invalidation: >> > + */ >> >> Ugh. If I'm reading this right, __flush_tlb_single() means "flush one >> user address" and __flush_tlb_one() means "flush one kernel address". > > That would make sense, woulnd't it? :-) But afaict the __flush_tlb_one() > user in tlb_uv.c is in fact for userspace and should be > __flush_tlb_single(). > > Andrew, Mike, can either of you shed light on what exactly you need > invalidated there? > >> That's, um, not exactly obvious. Could this be at least commented >> better? > > As is __flush_tlb_single() does user and __flush_tlb_one() does > user+kernel.
Yep. A one-liner above the function to that effect would make it *way* clearer what's going on.