From: Jerome Glisse <jglisse@redhat.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
dan.j.williams@intel.com, ldufour@linux.vnet.ibm.com
Subject: Re: [PATCH] mm/dev_pfn: Exclude MEMORY_DEVICE_PRIVATE while computing virtual address
Date: Mon, 20 May 2019 15:27:21 -0400 [thread overview]
Message-ID: <20190520192721.GA4049@redhat.com> (raw)
In-Reply-To: <cb8cbd57-9220-aba9-7579-dbcf35f02672@arm.com>
On Mon, May 20, 2019 at 11:07:38AM +0530, Anshuman Khandual wrote:
> On 05/18/2019 03:20 AM, Andrew Morton wrote:
> > On Fri, 17 May 2019 16:08:34 +0530 Anshuman Khandual <anshuman.khandual@arm.com> wrote:
> >
> >> The presence of struct page does not guarantee linear mapping for the pfn
> >> physical range. Device private memory which is non-coherent is excluded
> >> from linear mapping during devm_memremap_pages() though they will still
> >> have struct page coverage. Just check for device private memory before
> >> giving out virtual address for a given pfn.
> >
> > I was going to give my standard "what are the user-visible runtime
> > effects of this change?", but...
> >
> >> All these helper functions are all pfn_t related but could not figure out
> >> another way of determining a private pfn without looking into it's struct
> >> page. pfn_t_to_virt() is not getting used any where in mainline kernel.Is
> >> it used by out of tree drivers ? Should we then drop it completely ?
> >
> > Yeah, let's kill it.
> >
> > But first, let's fix it so that if someone brings it back, they bring
> > back a non-buggy version.
>
> Makes sense.
>
> >
> > So... what (would be) the user-visible runtime effects of this change?
>
> I am not very well aware about the user interaction with the drivers which
> hotplug and manage ZONE_DEVICE memory in general. Hence will not be able to
> comment on it's user visible runtime impact. I just figured this out from
> code audit while testing ZONE_DEVICE on arm64 platform. But the fix makes
> the function bit more expensive as it now involve some additional memory
> references.
A device private pfn can never leak outside code that does not understand it
So this change is useless for any existing users and i would like to keep the
existing behavior ie never leak device private pfn.
Cheers,
Jérôme
next prev parent reply other threads:[~2019-05-20 19:27 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-17 10:38 Anshuman Khandual
2019-05-17 21:50 ` Andrew Morton
2019-05-20 5:37 ` Anshuman Khandual
2019-05-20 19:00 ` Dan Williams
2019-05-20 19:27 ` Jerome Glisse [this message]
2019-05-20 19:33 ` Dan Williams
2019-05-21 2:08 ` Anshuman Khandual
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