linux-kernel - Re: Linux 4.18-rc7

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Message-ID: <20180801212518.jjdwf53p3sj4b455@kshutemo-mobl1>
Date:   Thu, 2 Aug 2018 00:25:18 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Tony Luck <tony.luck@...el.com>,
        Amit Pundir <amit.pundir@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Hugh Dickins <hughd@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        youling 257 <youling257@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Colin Cross <ccross@...gle.com>
Subject: Re: Linux 4.18-rc7

On Wed, Aug 01, 2018 at 01:56:19PM -0700, Linus Torvalds wrote:
> On Wed, Aug 1, 2018 at 1:52 PM Kirill A. Shutemov <kirill@...temov.name> wrote:
> >
> > Is there a reason why we pass vma to flush_tlb_range?
> 
> Yes. It's even in that patch.
> 
> The fact is, real MM users *have* a vma, and passing it in to the TLB
> flushing is the right thing to do. That allows architectures that care
> (mainly powerpc, I think) to notice that "hey, this range only had
> execute permissions, so I only need to flush the ITLB".
> 
> The people who use tlb_flush_range() any other way are doing an
> arch-specific hack.  It's not how tlb_flush_range() was defined, and
> it's not how you can use it in general.

Okay, I see.

ARM, unicore32 and xtensa avoid iTLB flush for non-executable VMAs.

> 
> > It's not obvious to me what information from VMA can be useful for an
> > implementation.
> 
> See the patch I sent, which had this as part of it:
> 
> -                * XXX fix me: flush_tlb_range() should take an mm
> pointer instead of a
> -                * vma pointer.
> +                * flush_tlb_range() takes a vma instead of a mm pointer because
> +                * some architectures want the vm_flags for ITLB/DTLB flush.
> 
> because I wanted to educate people about why the interface was what it
> was, and the "fixme" was bogus shit.

I didn't noticied this. Sorry.

-- 
 Kirill A. Shutemov