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SubjectRe: [RFC PATCH v3 1/2] mempinfd: Add new syscall to provide memory pin
On Mon, Feb 08, 2021 at 09:14:28AM +0100, David Hildenbrand wrote:

> People are constantly struggling with the effects of long term pinnings
> under user space control, like we already have with vfio and RDMA.
> And here we are, adding yet another, easier way to mess with core MM in the
> same way. This feels like a step backwards to me.

Yes, this seems like a very poor candidate to be a system call in this
format. Much too narrow, poorly specified, and possibly security
implications to allow any process whatsoever to pin memory.

I keep encouraging people to explore a standard shared SVA interface
that can cover all these topics (and no, uaccel is not that
interface), that seems much more natural.

I still haven't seen an explanation why DMA is so special here,
migration and so forth jitter the CPU too, environments that care
about jitter have to turn this stuff off.


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