lkml.org 
[lkml]   [2017]   [Dec]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [patch 51/60] x86/mm: Allow flushing for future ASID switches
    On Mon, Dec 4, 2017 at 2:47 PM, Peter Zijlstra <peterz@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.

    \
     
     \ /
      Last update: 2017-12-04 23:56    [W:4.090 / U:0.340 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site