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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, rkrcmar@redhat.com,
	alexander.h.duyck@linux.intel.com, x86@kernel.org,
	mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
	pbonzini@redhat.com, tglx@linutronix.de,
	akpm@linux-foundation.org
Subject: Re: [RFC PATCH 2/4] kvm: Add host side support for free memory hints
Date: Mon, 11 Feb 2019 12:48:35 -0500
Message-ID: <20190211124203-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <39c915a7-e317-db01-0286-579230f37da2@intel.com>

On Mon, Feb 11, 2019 at 09:41:19AM -0800, Dave Hansen wrote:
> On 2/9/19 4:44 PM, Michael S. Tsirkin wrote:
> > So the policy should not leak into host/guest interface.
> > Instead it is better to just keep the pages pinned and
> > ignore the hint for now.
> 
> It does seems a bit silly to have guests forever hinting about freed
> memory when the host never has a hope of doing anything about it.
> 
> Is that part fixable?


Yes just not with existing IOMMU APIs.

It's in the paragraph just above that you cut out:
	Yes right now assignment is not smart enough but generally
	you can protect the unused page in the IOMMU and that's it,
	it's safe.

So e.g.
	extern int iommu_remap(struct iommu_domain *domain, unsigned long iova,
				     phys_addr_t paddr, size_t size, int prot);


I can elaborate if you like but generally we would need an API that
allows you to atomically update a mapping for a specific page without
perturbing the mapping for other pages.

-- 
MST

  reply index

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-04 18:15 [RFC PATCH 0/4] kvm: Report unused guest pages to host Alexander Duyck
2019-02-04 18:15 ` [RFC PATCH 1/4] madvise: Expose ability to set dontneed from kernel Alexander Duyck
2019-02-04 18:15 ` [RFC PATCH 2/4] kvm: Add host side support for free memory hints Alexander Duyck
2019-02-10  0:44   ` Michael S. Tsirkin
2019-02-11 17:34     ` Alexander Duyck
2019-02-11 17:36       ` Michael S. Tsirkin
2019-02-11 17:41     ` Dave Hansen
2019-02-11 17:48       ` Michael S. Tsirkin [this message]
2019-02-11 18:30         ` Alexander Duyck
2019-02-11 19:24           ` Michael S. Tsirkin
2019-02-04 18:15 ` [RFC PATCH 3/4] kvm: Add guest " Alexander Duyck
2019-02-04 19:44   ` Dave Hansen
2019-02-04 20:42     ` Alexander Duyck
2019-02-04 23:00   ` Nadav Amit
2019-02-04 23:37     ` Alexander Duyck
2019-02-05  0:03       ` Nadav Amit
2019-02-05  0:16         ` Alexander Duyck
2019-02-05  1:46           ` Nadav Amit
2019-02-05 18:09             ` Alexander Duyck
2019-02-07 18:21   ` Luiz Capitulino
2019-02-07 18:44     ` Alexander Duyck
2019-02-07 20:02       ` Luiz Capitulino
2019-02-08 21:05       ` Nitesh Narayan Lal
2019-02-08 21:31         ` Alexander Duyck
2019-02-10  0:49   ` Michael S. Tsirkin
2019-02-11 16:31     ` Alexander Duyck
2019-02-11 17:36       ` Michael S. Tsirkin
2019-02-11 18:10         ` Alexander Duyck
2019-02-11 19:54           ` Michael S. Tsirkin
2019-02-11 21:00             ` Alexander Duyck
2019-02-11 22:52               ` Michael S. Tsirkin
     [not found]                 ` <94462313ccd927d25675f69de459456cf066c1a2.camel@linux.intel.com>
2019-02-12  0:34                   ` Michael S. Tsirkin
2019-02-11 17:48     ` Dave Hansen
2019-02-11 17:58       ` Michael S. Tsirkin
2019-02-11 18:19         ` Dave Hansen
2019-02-11 19:56           ` Michael S. Tsirkin
2019-02-04 18:15 ` [RFC PATCH 4/4] mm: Add merge page notifier Alexander Duyck
2019-02-04 19:40   ` Dave Hansen
2019-02-04 19:51     ` Alexander Duyck
2019-02-10  0:57   ` Michael S. Tsirkin
2019-02-11 13:30     ` Nitesh Narayan Lal
2019-02-11 14:17       ` Michael S. Tsirkin
2019-02-11 16:24         ` Nitesh Narayan Lal
2019-02-11 17:41           ` Michael S. Tsirkin
2019-02-11 18:09             ` Nitesh Narayan Lal
2019-02-11  6:40   ` Aaron Lu
2019-02-11 15:58     ` Alexander Duyck
2019-02-12  2:09       ` Aaron Lu
2019-02-12 17:20         ` Alexander Duyck
2019-02-04 18:19 ` [RFC PATCH QEMU] i386/kvm: Enable paravirtual unused page hint mechanism Alexander Duyck
2019-02-05 17:25 ` [RFC PATCH 0/4] kvm: Report unused guest pages to host Nitesh Narayan Lal
2019-02-05 18:43   ` Alexander Duyck
2019-02-07 14:48 ` Nitesh Narayan Lal
2019-02-07 16:56   ` Alexander Duyck
2019-02-10  0:51 ` Michael S. Tsirkin

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