linux-kernel - Re: [PATCH 6/6] x86/xen: open code alloc_vm_area in arch_gnttab

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Message-ID: <20200922152706.GA30633@lst.de>
Date:   Tue, 22 Sep 2020 17:27:06 +0200
From:   Christoph Hellwig <hch@....de>
To:     boris.ostrovsky@...cle.com
Cc:     Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Minchan Kim <minchan@...nel.org>,
        Nitin Gupta <ngupta@...are.org>, x86@...nel.org,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 6/6] x86/xen: open code alloc_vm_area in
 arch_gnttab_valloc

On Tue, Sep 22, 2020 at 11:24:20AM -0400, boris.ostrovsky@...cle.com wrote:
> 
> On 9/22/20 10:58 AM, Christoph Hellwig wrote:
> > On Mon, Sep 21, 2020 at 04:44:10PM -0400, boris.ostrovsky@...cle.com wrote:
> >> This will end up incrementing area->ptes pointer. So perhaps something like
> >>
> >>
> >> pte_t **ptes = area->ptes;
> >>
> >> if (apply_to_page_range(&init_mm, (unsigned long)area->area->addr,
> >>                         PAGE_SIZE * nr_frames, gnttab_apply, &ptes)) {
> >>
> >>        ...
> > Yeah.  What do you think of this version? 
> 
> 
> Oh yes, this is way better. This now can actually be read without trying to mentally unwind triple pointers. (You probably want to initialize idx to zero before calling apply_to_page_range(), I am not sure it's guaranteed to be zero).

Both instances are static variables, thus in .bss and initialized.
So unless you insist I don't think we need a manual one.