From: Dan Williams <dan.j.williams@intel.com>
To: alexander.h.duyck@linux.intel.com
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
"Zhang Yi" <yi.z.zhang@linux.intel.com>,
"Barret Rhoden" <brho@google.com>,
"KVM list" <kvm@vger.kernel.org>,
linux-nvdimm <linux-nvdimm@lists.01.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Linux MM" <linux-mm@kvack.org>,
"Dave Jiang" <dave.jiang@intel.com>,
"Zhang, Yu C" <yu.c.zhang@intel.com>,
"Pankaj Gupta" <pagupta@redhat.com>,
"David Hildenbrand" <david@redhat.com>, "Jan Kara" <jack@suse.cz>,
"Christoph Hellwig" <hch@lst.de>,
rkrcmar@redhat.com, "Jérôme Glisse" <jglisse@redhat.com>
Subject: Re: [PATCH RFC 2/3] mm: Add support for exposing if dev_pagemap supports refcount pinning
Date: Mon, 3 Dec 2018 12:31:08 -0800 [thread overview]
Message-ID: <CAPcyv4i=FL4f34H2_1mgWMk=UyyaXFaKPh5zJSnFNyN3cBoJhA@mail.gmail.com> (raw)
In-Reply-To: <97943d2ed62e6887f4ba51b985ef4fb5478bc586.camel@linux.intel.com>
On Mon, Dec 3, 2018 at 12:21 PM Alexander Duyck
<alexander.h.duyck@linux.intel.com> wrote:
>
> On Mon, 2018-12-03 at 11:47 -0800, Dan Williams wrote:
> > On Mon, Dec 3, 2018 at 11:25 AM Alexander Duyck
> > <alexander.h.duyck@linux.intel.com> wrote:
> > >
> > > Add a means of exposing if a pagemap supports refcount pinning. I am doing
> > > this to expose if a given pagemap has backing struct pages that will allow
> > > for the reference count of the page to be incremented to lock the page
> > > into place.
> > >
> > > The KVM code already has several spots where it was trying to use a
> > > pfn_valid check combined with a PageReserved check to determien if it could
> > > take a reference on the page. I am adding this check so in the case of the
> > > page having the reserved flag checked we can check the pagemap for the page
> > > to determine if we might fall into the special DAX case.
> > >
> > > Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> > > ---
> > > drivers/nvdimm/pfn_devs.c | 2 ++
> > > include/linux/memremap.h | 5 ++++-
> > > include/linux/mm.h | 11 +++++++++++
> > > 3 files changed, 17 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c
> > > index 6f22272e8d80..7a4a85bcf7f4 100644
> > > --- a/drivers/nvdimm/pfn_devs.c
> > > +++ b/drivers/nvdimm/pfn_devs.c
> > > @@ -640,6 +640,8 @@ static int __nvdimm_setup_pfn(struct nd_pfn *nd_pfn, struct dev_pagemap *pgmap)
> > > } else
> > > return -ENXIO;
> > >
> > > + pgmap->support_refcount_pinning = true;
> > > +
> >
> > There should be no dev_pagemap instance instance where this isn't
> > true, so I'm missing why this is needed?
>
> I thought in the case of HMM there were instances where you couldn't
> pin the page, isn't there? Specifically I am thinking of the definition
> of MEMORY_DEVICE_PUBLIC:
> Device memory that is cache coherent from device and CPU point of
> view. This is use on platform that have an advance system bus (like
> CAPI or CCIX). A driver can hotplug the device memory using
> ZONE_DEVICE and with that memory type. Any page of a process can be
> migrated to such memory. However no one should be allow to pin such
> memory so that it can always be evicted.
>
> It sounds like MEMORY_DEVICE_PUBLIC and MMIO would want to fall into
> the same category here in order to allow a hot-plug event to remove the
> device and take the memory with it, or is my understanding on this not
> correct?
I don't understand how HMM expects to enforce no pinning, but in any
event it should always be the expectation an elevated reference count
on a page prevents that page from disappearing. Anything else is
broken.
next prev parent reply other threads:[~2018-12-03 20:31 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-03 19:25 [PATCH RFC 0/3] Fix KVM misinterpreting Reserved page as an MMIO page Alexander Duyck
2018-12-03 19:25 ` [PATCH RFC 1/3] kvm: Split use cases for kvm_is_reserved_pfn to kvm_is_refcounted_pfn Alexander Duyck
2018-12-03 19:25 ` [PATCH RFC 2/3] mm: Add support for exposing if dev_pagemap supports refcount pinning Alexander Duyck
2018-12-03 19:47 ` Dan Williams
2018-12-03 20:21 ` Alexander Duyck
2018-12-03 20:31 ` Dan Williams [this message]
2018-12-03 20:53 ` Alexander Duyck
2018-12-03 21:05 ` Dan Williams
2018-12-03 21:50 ` Alexander Duyck
2018-12-04 19:08 ` Dan Williams
2018-12-04 22:51 ` Alexander Duyck
2018-12-04 23:24 ` Barret Rhoden
2018-12-05 0:01 ` Alexander Duyck
2018-12-05 0:26 ` Dan Williams
2018-12-05 8:13 ` David Hildenbrand
2018-12-03 19:25 ` [PATCH RFC 3/3] kvm: Add additional check to determine if a page is refcounted Alexander Duyck
2018-12-04 6:59 ` [PATCH RFC 0/3] Fix KVM misinterpreting Reserved page as an MMIO page Yi Zhang
2018-12-04 18:45 ` Alexander Duyck
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