linux-kernel - Re: [RFC][Patch v8 0/7] KVM: Guest Free Page Hinting

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <0118482c-e633-3949-6797-94d7deb8a382@redhat.com>
Date:   Tue, 19 Feb 2019 21:02:52 +0100
From:   David Hildenbrand <david@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Alexander Duyck <alexander.duyck@...il.com>
Cc:     Nitesh Narayan Lal <nitesh@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>, lcapitulino@...hat.com,
        pagupta@...hat.com, wei.w.wang@...el.com,
        Yang Zhang <yang.zhang.wz@...il.com>,
        Rik van Riel <riel@...riel.com>, dodgen@...gle.com,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        dhildenb@...hat.com, Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC][Patch v8 0/7] KVM: Guest Free Page Hinting

On 19.02.19 20:58, Michael S. Tsirkin wrote:
> On Tue, Feb 19, 2019 at 10:06:35AM -0800, Alexander Duyck wrote:
>>> I tend to like an asynchronous reporting approach as discussed in this
>>> thread, we would have to see if Nitesh could get it implemented.
>>
>> I agree it would be great if it could work. However I have concerns
>> given that work on this patch set dates back to 2017, major issues
>> such as working around device assignment have yet to be addressed,
> 
> BTW for device assignment to work, your idea of sending
> data directly to kvm won't work, will it?
> You need to update userspace so it can update VFIO right?
> Another blocker for assignment is ability to make holes
> an an existing mapping - supported by hardware but
> not by IOMMU drivers.

I had the exact same thought and then realized that we decided to block
the balloon in user space until we figured out how to handle this properly.

I wonder if MADV_FREE behaves differently compared to MADV_DONTNEED when
finding pinned pages, but I doubt it. Most probably we'll have to
disable hinting for device assignments as well.

> 
> All the issues are shared with balloon btw, so that
> could be another reason to use the balloon.

Yes, smells like it.

-- 

Thanks,

David / dhildenb