linux-kernel - Re: [PATCH v4 2/2] vfio/type1: Prune vfio_pin_page

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Message-ID: <20170417065420.GD16703@pxdev.xzpeter.org>
Date:   Mon, 17 Apr 2017 14:54:21 +0800
From:   Peter Xu <peterx@...hat.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     kvm@...r.kernel.org, eric.auger@...hat.com, kwankhede@...dia.com,
        linux-kernel@...r.kernel.org, slp@...hat.com
Subject: Re: [PATCH v4 2/2] vfio/type1: Prune vfio_pin_page_external()

On Sun, Apr 16, 2017 at 07:42:39PM -0600, Alex Williamson wrote:
> With vfio_lock_acct() testing the locked memory limit under mmap_sem,
> it's redundant to do it here for a single page.  We can also reorder
> our tests such that we can avoid testing for reserved pages if we're
> not doing accounting, and test the process CAP_IPC_LOCK only if we
> are doing accounting.  Finally, this function oddly returns 1 on
> success.  Update to return zero on success, -errno on error.  Since
> the function only pins a single page, there's no need to return the
> number of pages pinned.
> 
> N.B. vfio_pin_pages_remote() can pin a large contiguous range of pages
> before calling vfio_lock_acct().  If we were to similarly remove the
> extra test there, a user could temporarily pin far more pages than
> they're allowed.
> 
> Suggested-by: Kirti Wankhede <kwankhede@...dia.com>
> Suggested-by: Peter Xu <peterx@...hat.com>

Maybe this suggested-by honor should be for Kirti only? :)

For the patch, I think it's good to me as long as we have the
accounting check in vfio_lock_acct() which is just introduced in
previous patch, so:

Reviewed-by: Peter Xu <peterx@...hat.com>

Thanks!

-- 
Peter Xu