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From: Andy Lutomirski <luto@kernel.org>
Date: Mon, 4 Dec 2017 14:36:13 -0800
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Subject: Re: [patch 51/60] x86/mm: Allow flushing for future ASID switches
To: Dave Hansen <dave.hansen@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bpetkov@suse.de>,
        Greg KH <gregkh@linuxfoundation.org>, Kees Cook <keescook@google.com>,
        Hugh Dickins <hughd@google.com>, Brian Gerst <brgerst@gmail.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Denys Vlasenko <dvlasenk@redhat.com>, Rik van Riel <riel@redhat.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        David Laight <David.Laight@aculab.com>,
        Eduardo Valentin <eduval@amazon.com>, aliguori@amazon.com,
        Will Deacon <will.deacon@arm.com>,
        Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@kernel.org>, michael.schwarz@iaik.tugraz.at,
        Borislav Petkov <bp@alien8.de>, moritz.lipp@iaik.tugraz.at,
        richard.fellner@student.tugraz.at
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On Mon, Dec 4, 2017 at 2:34 PM, Dave Hansen <dave.hansen@intel.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