linux-kernel - Re: [patch 51/60] x86/mm: Allow flushing for future ASID switches

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Date:   Mon, 4 Dec 2017 14:36:13 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>, aliguori@...zon.com,
        Will Deacon <will.deacon@....com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>, michael.schwarz@...k.tugraz.at,
        Borislav Petkov <bp@...en8.de>, moritz.lipp@...k.tugraz.at,
        richard.fellner@...dent.tugraz.at
Subject: Re: [patch 51/60] x86/mm: Allow flushing for future ASID switches

On Mon, Dec 4, 2017 at 2:34 PM, Dave Hansen <dave.hansen@...el.com> wrote:
> On 12/04/2017 02:22 PM, Andy Lutomirski wrote:
>>> +
>>> +       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);
>>         }
>
> We have loops like this:
>
>         for (addr = start; addr < end; addr += PAGE_SIZE)
>                 flush_tlb_single();

Couldn't we just make those looks more intelligent:

for (...)
  flush_tlb_kernelmode_single(...);

if (kpti)
  invalidate_asid_other();

(Isn't there only one such look now, in flush_tlb_func_common()?)

--Andy