linux-kernel - Re: [PATCH v3 07/33] nds32: MMU initialization

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Date:   Mon, 18 Dec 2017 20:22:54 +0800
From:   Guo Ren <ren_guo@...ky.com>
To:     Greentime Hu <green.hu@...il.com>
Cc:     Greentime <greentime@...estech.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Rob Herring <robh+dt@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Vincent Chen <deanbo422@...il.com>,
        DTML <devicetree@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-serial@...r.kernel.org,
        Geert Uytterhoeven <geert.uytterhoeven@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>, Greg KH <greg@...ah.com>,
        Vincent Chen <vincentc@...estech.com>
Subject: Re: [PATCH v3 07/33] nds32: MMU initialization

On Mon, Dec 18, 2017 at 07:21:30PM +0800, Greentime Hu wrote:
> Hi, Guo Ren:
> 
> 2017-12-18 17:08 GMT+08:00 Guo Ren <ren_guo@...ky.com>:
> > Hi Greentime,
> >
> > On Fri, Dec 08, 2017 at 05:11:50PM +0800, Greentime Hu wrote:
> > [...]
> >>
> >> diff --git a/arch/nds32/mm/highmem.c b/arch/nds32/mm/highmem.c
> > [...]
> >> +void *kmap(struct page *page)
> >> +{
> >> +     unsigned long vaddr;
> >> +     might_sleep();
> >> +     if (!PageHighMem(page))
> >> +             return page_address(page);
> >> +     vaddr = (unsigned long)kmap_high(page);
> > Here should invalid the cpu_mmu_tlb's entry, Or invalid it in the
> > set_pte().
> >
> > eg:
> > vaddr0 = kmap(page0)
> > *vaddr0 = val0 //It will cause tlb-miss, and hard-refill to MMU-tlb
> > kunmap(page0)
> > vaddr1 = kmap(page1) // Mostly vaddr1 = vaddr0
> > val = vaddr1; //No tlb-miss and it will get page0's val not page1, because
> >                 last expired vaddr0's entry is left in CPU-MMU-tlb.
> >
> 
> Thanks.
> I will add __nds32__tlbop_inv(vaddr); to invalidate this mapping
> before retrun vaddr.

Sorry, perhaps I'm wrong. See
kmap->kmap_high->map_new_virtual->get_next_pkmap_nr(color).

Seems pkmap will return the vaddr by vaddr + 1 until
no_more_pkmaps(), and then flush_all_zero_pkmaps.
Just kmap_atomic need it, and you've done.

But I don't know why mips need flush_tlb_one in
arch/mips/mm/highmem.c:kmap(). VIPT? but kmap give the get_pkmap_color
for aliasing.

Best Regards
 Guo Ren