From: Barret Rhoden <brho@google.com>
To: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>,
"Zhang, Yu C <yu.c.zhang@intel.com>,
KVM list <kvm@vger.kernel.org>,
linux-nvdimm" <linux-nvdimm@lists.01.org>,
"Jan Kara" <jack@suse.cz>, "David Hildenbrand" <david@redhat.com>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Linux MM" <linux-mm@kvack.org>,
rkrcmar@redhat.com, "Paolo Bonzini" <pbonzini@redhat.com>,
"Christoph Hellwig" <hch@lst.de>
Subject: Re: [PATCH RFC 2/3] mm: Add support for exposing if dev_pagemap supports refcount pinning
Date: Tue, 4 Dec 2018 18:24:28 -0500 [thread overview]
Message-ID: <20181204182428.11bec385@gnomeregan.cam.corp.google.com> (raw)
In-Reply-To: <dd7296db5996f15cc3e666d008f209f5f24fa98e.camel@linux.intel.com>
Hi -
On 2018-12-04 at 14:51 Alexander Duyck
<alexander.h.duyck@linux.intel.com> wrote:
[snip]
> > I think the confusion arises from the fact that there are a few MMIO
> > resources with a struct page and all the rest MMIO resources without.
> > The problem comes from the coarse definition of pfn_valid(), it may
> > return 'true' for things that are not System-RAM, because pfn_valid()
> > may be something as simplistic as a single "address < X" check. Then
> > PageReserved is a fallback to clarify the pfn_valid() result. The
> > typical case is that MMIO space is not caught up in this linear map
> > confusion. An MMIO address may or may not have an associated 'struct
> > page' and in most cases it does not.
>
> Okay. I think I understand this somewhat now. So the page might be
> physically there, but with the reserved bit it is not supposed to be
> touched.
>
> My main concern with just dropping the bit is that we start seeing some
> other uses that I was not certain what the impact would be. For example
> the functions like kvm_set_pfn_accessed start going in and manipulating
> things that I am not sure should be messed with for a DAX page.
One thing regarding the accessed and dirty bits is that we might want
to have DAX pages marked dirty/accessed, even if we can't LRU-reclaim
or swap them. I don't have a real example and I'm fairly ignorant
about the specifics here. But one possibility would be using the A/D
bits to detect changes to a guest's memory for VM migration. Maybe
there would be issues with KSM too.
Barret
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next prev parent reply other threads:[~2018-12-04 23:24 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
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 [this message]
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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