From: Haozhong Zhang <haozhong.zhang@intel.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Juergen Gross <jgross@suse.com>, Wei Liu <wei.liu2@citrix.com>,
Kevin Tian <kevin.tian@intel.com>, Keir Fraser <keir@xen.org>,
Ian Campbell <ian.campbell@citrix.com>,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>,
xen-devel@lists.xen.org, Jan Beulich <jbeulich@suse.com>,
Jun Nakajima <jun.nakajima@intel.com>,
Xiao Guangrong <guangrong.xiao@linux.intel.com>
Subject: Re: [RFC Design Doc] Add vNVDIMM support for Xen
Date: Thu, 4 Feb 2016 10:36:54 +0800 [thread overview]
Message-ID: <20160204023654.GA4066@hz-desktop.sh.intel.com> (raw)
In-Reply-To: <20160203154744.GG20732@char.us.oracle.com>
On 02/03/16 10:47, Konrad Rzeszutek Wilk wrote:
> > > > > Open: It seems no system call/ioctl is provided by Linux kernel to
> > > > > get the physical address from a virtual address.
> > > > > /proc/<qemu_pid>/pagemap provides information of mapping from
> > > > > VA to PA. Is it an acceptable solution to let QEMU parse this
> > > > > file to get the physical address?
> > > >
> > > > Does it work in a non-root scenario?
> > > >
> > >
> > > Seemingly no, according to Documentation/vm/pagemap.txt in Linux kernel:
> > > | Since Linux 4.0 only users with the CAP_SYS_ADMIN capability can get PFNs.
> > > | In 4.0 and 4.1 opens by unprivileged fail with -EPERM. Starting from
> > > | 4.2 the PFN field is zeroed if the user does not have CAP_SYS_ADMIN.
> > > | Reason: information about PFNs helps in exploiting Rowhammer vulnerability.
>
> Ah right.
> > >
> > > A possible alternative is to add a new hypercall similar to
> > > XEN_DOMCTL_memory_mapping but receiving virtual address as the address
> > > parameter and translating to machine address in the hypervisor.
> >
> > That might work.
>
> That won't work.
>
> This is a userspace VMA - which means the once the ioctl is done we swap
> to kernel virtual addresses. Now we may know that the prior cr3 has the
> userspace virtual address and walk it down - but what if the domain
> that is doing this is PVH? (or HVM) - the cr3 of userspace is tucked somewhere
> inside the kernel.
>
> Which means this hypercall would need to know the Linux kernel task structure
> to find this.
>
Thanks for pointing out this. Really it's not a workable solution.
> May I propose another solution - an stacking driver (similar to loop). You
> setup it up (ioctl /dev/pmem0/guest.img, get some /dev/mapper/guest.img created).
> Then mmap the /dev/mapper/guest.img - all of the operations are the same - except
> it may have an extra ioctl - get_pfns - which would provide the data in similar
> form to pagemap.txt.
>
I'll have a look at this, thanks!
> But folks will then ask - why don't you just use pagemap? Could the pagemap
> have an extra security capability check? One that can be set for
> QEMU?
>
Basically for the concern on whether non-root QEMU could work as in
Stefano's comments.
> >
> >
> > > > > Open: For a large pmem, mmap(2) is very possible to not map all SPA
> > > > > occupied by pmem at the beginning, i.e. QEMU may not be able to
> > > > > get all SPA of pmem from buf (in virtual address space) when
> > > > > calling XEN_DOMCTL_memory_mapping.
> > > > > Can mmap flag MAP_LOCKED or mlock(2) be used to enforce the
> > > > > entire pmem being mmaped?
> > > >
> > > > Ditto
> > > >
> > >
> > > No. If I take the above alternative for the first open, maybe the new
> > > hypercall above can inject page faults into dom0 for the unmapped
> > > virtual address so as to enforce dom0 Linux to create the page
> > > mapping.
>
> Ugh. That sounds hacky. And you wouldn't neccessarily be safe.
> Imagine that the system admin decides to defrag the /dev/pmem filesystem.
> Or move the files (disk images) around. If they do that - we may
> still have the guest mapped to system addresses which may contain filesystem
> metadata now, or a different guest image. We MUST mlock or lock the file
> during the duration of the guest.
>
>
So mlocking or locking the mmaped file, or other ways to 'pin' the
mmaped file on pmem is a necessity.
Thanks,
Haozhong
next prev parent reply other threads:[~2016-02-04 2:36 UTC|newest]
Thread overview: 121+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-01 5:44 [RFC Design Doc] Add vNVDIMM support for Xen Haozhong Zhang
2016-02-01 18:25 ` Andrew Cooper
2016-02-02 3:27 ` Tian, Kevin
2016-02-02 3:44 ` Haozhong Zhang
2016-02-02 11:09 ` Andrew Cooper
2016-02-02 6:33 ` Tian, Kevin
2016-02-02 7:39 ` Zhang, Haozhong
2016-02-02 7:48 ` Tian, Kevin
2016-02-02 7:53 ` Zhang, Haozhong
2016-02-02 8:03 ` Tian, Kevin
2016-02-02 8:49 ` Zhang, Haozhong
2016-02-02 19:01 ` Konrad Rzeszutek Wilk
2016-02-02 17:11 ` Stefano Stabellini
2016-02-03 7:00 ` Haozhong Zhang
2016-02-03 9:13 ` Jan Beulich
2016-02-03 14:09 ` Andrew Cooper
2016-02-03 14:23 ` Haozhong Zhang
2016-02-05 14:40 ` Ross Philipson
2016-02-06 1:43 ` Haozhong Zhang
2016-02-06 16:17 ` Ross Philipson
2016-02-03 12:02 ` Stefano Stabellini
2016-02-03 13:11 ` Haozhong Zhang
2016-02-03 14:20 ` Andrew Cooper
2016-02-04 3:10 ` Haozhong Zhang
2016-02-03 15:16 ` George Dunlap
2016-02-03 15:22 ` Stefano Stabellini
2016-02-03 15:35 ` Konrad Rzeszutek Wilk
2016-02-03 15:35 ` George Dunlap
2016-02-04 2:55 ` Haozhong Zhang
2016-02-04 12:24 ` Stefano Stabellini
2016-02-15 3:16 ` Zhang, Haozhong
2016-02-16 11:14 ` Stefano Stabellini
2016-02-16 12:55 ` Jan Beulich
2016-02-17 9:03 ` Haozhong Zhang
2016-03-04 7:30 ` Haozhong Zhang
2016-03-16 12:55 ` Haozhong Zhang
2016-03-16 13:13 ` Konrad Rzeszutek Wilk
2016-03-16 13:16 ` Jan Beulich
2016-03-16 13:55 ` Haozhong Zhang
2016-03-16 14:23 ` Jan Beulich
2016-03-16 14:55 ` Haozhong Zhang
2016-03-16 15:23 ` Jan Beulich
2016-03-17 8:58 ` Haozhong Zhang
2016-03-17 11:04 ` Jan Beulich
2016-03-17 12:44 ` Haozhong Zhang
2016-03-17 12:59 ` Jan Beulich
2016-03-17 13:29 ` Haozhong Zhang
2016-03-17 13:52 ` Jan Beulich
2016-03-17 14:00 ` Ian Jackson
2016-03-17 14:21 ` Haozhong Zhang
2016-03-29 8:47 ` Haozhong Zhang
2016-03-29 9:11 ` Jan Beulich
2016-03-29 10:10 ` Haozhong Zhang
2016-03-29 10:49 ` Jan Beulich
2016-04-08 5:02 ` Haozhong Zhang
2016-04-08 15:52 ` Jan Beulich
2016-04-12 8:45 ` Haozhong Zhang
2016-04-21 5:09 ` Haozhong Zhang
2016-04-21 7:04 ` Jan Beulich
2016-04-22 2:36 ` Haozhong Zhang
2016-04-22 8:24 ` Jan Beulich
2016-04-22 10:16 ` Haozhong Zhang
2016-04-22 10:53 ` Jan Beulich
2016-04-22 12:26 ` Haozhong Zhang
2016-04-22 12:36 ` Jan Beulich
2016-04-22 12:54 ` Haozhong Zhang
2016-04-22 13:22 ` Jan Beulich
2016-03-17 13:32 ` Konrad Rzeszutek Wilk
2016-02-03 15:47 ` Konrad Rzeszutek Wilk
2016-02-04 2:36 ` Haozhong Zhang [this message]
2016-02-15 9:04 ` Zhang, Haozhong
2016-02-02 19:15 ` Konrad Rzeszutek Wilk
2016-02-03 8:28 ` Haozhong Zhang
2016-02-03 9:18 ` Jan Beulich
2016-02-03 12:22 ` Haozhong Zhang
2016-02-03 12:38 ` Jan Beulich
2016-02-03 12:49 ` Haozhong Zhang
2016-02-03 14:30 ` Andrew Cooper
2016-02-03 14:39 ` Jan Beulich
2016-02-15 8:43 ` Haozhong Zhang
2016-02-15 11:07 ` Jan Beulich
2016-02-17 9:01 ` Haozhong Zhang
2016-02-17 9:08 ` Jan Beulich
2016-02-18 7:42 ` Haozhong Zhang
2016-02-19 2:14 ` Konrad Rzeszutek Wilk
2016-03-01 7:39 ` Haozhong Zhang
2016-03-01 18:33 ` Ian Jackson
2016-03-01 18:49 ` Konrad Rzeszutek Wilk
2016-03-02 7:14 ` Haozhong Zhang
2016-03-02 13:03 ` Jan Beulich
2016-03-04 2:20 ` Haozhong Zhang
2016-03-08 9:15 ` Haozhong Zhang
2016-03-08 9:27 ` Jan Beulich
2016-03-09 12:22 ` Haozhong Zhang
2016-03-09 16:17 ` Jan Beulich
2016-03-10 3:27 ` Haozhong Zhang
2016-03-17 11:05 ` Ian Jackson
2016-03-17 13:37 ` Haozhong Zhang
2016-03-17 13:56 ` Jan Beulich
2016-03-17 14:22 ` Haozhong Zhang
2016-03-17 14:12 ` Xu, Quan
2016-03-17 14:22 ` Zhang, Haozhong
2016-03-07 20:53 ` Konrad Rzeszutek Wilk
2016-03-08 5:50 ` Haozhong Zhang
2016-02-18 17:17 ` Jan Beulich
2016-02-24 13:28 ` Haozhong Zhang
2016-02-24 14:00 ` Ross Philipson
2016-02-24 16:42 ` Haozhong Zhang
2016-02-24 17:50 ` Ross Philipson
2016-02-24 14:24 ` Jan Beulich
2016-02-24 15:48 ` Haozhong Zhang
2016-02-24 16:54 ` Jan Beulich
2016-02-28 14:48 ` Haozhong Zhang
2016-02-29 9:01 ` Jan Beulich
2016-02-29 9:45 ` Haozhong Zhang
2016-02-29 10:12 ` Jan Beulich
2016-02-29 11:52 ` Haozhong Zhang
2016-02-29 12:04 ` Jan Beulich
2016-02-29 12:22 ` Haozhong Zhang
2016-03-01 13:51 ` Ian Jackson
2016-03-01 15:04 ` Jan Beulich
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