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Subject: Re: [PATCH] mm: Add new vma flag VM_LOCAL_CPU
To:     Matthew Wilcox <willy@infradead.org>
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CC:     Jeff Moyer <jmoyer@redhat.com>,
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From:   Boaz Harrosh <boazh@netapp.com>
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Date:   Tue, 15 May 2018 16:29:22 +0300
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On 15/05/18 15:03, Matthew Wilcox wrote:
> On Tue, May 15, 2018 at 02:41:41PM +0300, Boaz Harrosh wrote:
>> That would be very hard. Because that program would:
>> - need to be root
>> - need to start and pretend it is zus Server with the all mount
>>   thread thing, register new filesystem, grab some pmem devices.
>> - Mount the said filesystem on said pmem. Create core-pinned ZT threads
>>   for all CPUs, start accepting IO.
>> - And only then it can start leaking the pointer and do bad things.
> 
> All of these things you've done for me by writing zus Server.  All I
> have to do now is compromise zus Server.
> 
>>   The bad things it can do to the application, not to the Kernel.
>>   And as a full filesystem it can do those bad things to the application
>>   through the front door directly not needing the mismatch tlb at all.
> 
> That's not true.  When I have a TLB entry that points to a page of kernel
> ram, I can do almost anything, depending on what the kernel decides to
> do with that ram next.  Maybe it's page cache again, in which case I can
> affect whatever application happens to get it allocated.  Maybe it's a
> kmalloc page next, in which case I can affect any part of the kernel.
> Maybe it's a page table, then I can affect any process.
> 
>> That said. It brings up a very important point that I wanted to talk about.
>> In this design the zuf(Kernel) and the zus(um Server) are part of the distribution.
>> I would like to have the zus module be signed by the distro's Kernel's key and
>> checked on loadtime. I know there is an effort by Redhat guys to try and sign all
>> /sbin/* servers and have Kernel check these. So this is not the first time people
>> have thought about that.
> 
> You're getting dangerously close to admitting that the entire point
> of this exercise is so that you can link non-GPL NetApp code into the
> kernel in clear violation of the GPL.
> 

It is not that at all. What I'm trying to do is enable a zero-copy,
synchronous, low latency, low overhead. highly parallel - a new modern
interface with application servers.

You yourself had such a project that could easily be served out-of-the-box
with zufs, of a device that wanted to sit in user-mode.

Sometimes it is very convenient and needed for Servers to sit in
user-mode. And this interface allows that. And it is not always
a licensing thing. Though yes licensing is also an issue sometimes.
It is the reality we are living in.

But please indulge me I am curious how the point of signing /sbin/
servers, made you think about GPL licensing issues?

That said, is your point that as long as user-mode servers are sloooowwww
they are OK to be supported but if they are as fast as the kernel,
(as demonstrated a zufs based FS was faster then xfs-dax on same pmem)
Then it is a GPL violation?

Thanks
Boaz