Re: [PATCH v5 06/17] virt: acrn: Introduce VM management interfaces

[Shuo A Liu]

On Thu  5.Nov'20 at 10:16:45 +0100, Greg Kroah-Hartman wrote:
> On Thu, Nov 05, 2020 at 05:02:00PM +0800, Shuo A Liu wrote:
> > On Thu  5.Nov'20 at  9:26:39 +0100, Greg Kroah-Hartman wrote:
> > > On Thu, Nov 05, 2020 at 03:35:45PM +0800, Shuo A Liu wrote:
> > > > On Thu  5.Nov'20 at  7:29:07 +0100, Greg Kroah-Hartman wrote:
> > > > > On Thu, Nov 05, 2020 at 11:10:29AM +0800, Shuo A Liu wrote:
> > > > > > On Wed  4.Nov'20 at 20:02:35 +0100, Greg Kroah-Hartman wrote:
> > > > > > > On Mon, Oct 19, 2020 at 02:17:52PM +0800, shuo.a.liu@xxxxxxxxx wrote:
> > > > > > > > --- /dev/null
> > > > > > > > +++ b/include/uapi/linux/acrn.h
> > > > > > > > @@ -0,0 +1,56 @@
> > > > > > > > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > > > > > > > +/*
> > > > > > > > + * Userspace interface for /dev/acrn_hsm - ACRN Hypervisor Service Module
> > > > > > > > + *
> > > > > > > > + * This file can be used by applications that need to communicate with the HSM
> > > > > > > > + * via the ioctl interface.
> > > > > > > > + */
> > > > > > > > +
> > > > > > > > +#ifndef _UAPI_ACRN_H
> > > > > > > > +#define _UAPI_ACRN_H
> > > > > > > > +
> > > > > > > > +#include <linux/types.h>
> > > > > > > > +
> > > > > > > > +/**
> > > > > > > > + * struct acrn_vm_creation - Info to create a User VM
> > > > > > > > + * @vmid:		User VM ID returned from the hypervisor
> > > > > > > > + * @reserved0:		Reserved
> > > > > > > > + * @vcpu_num:		Number of vCPU in the VM. Return from hypervisor.
> > > > > > > > + * @reserved1:		Reserved
> > > > > > > > + * @uuid:		UUID of the VM. Pass to hypervisor directly.
> > > > > > > > + * @vm_flag:		Flag of the VM creating. Pass to hypervisor directly.
> > > > > > > > + * @ioreq_buf:		Service VM GPA of I/O request buffer. Pass to
> > > > > > > > + *			hypervisor directly.
> > > > > > > > + * @cpu_affinity:	CPU affinity of the VM. Pass to hypervisor directly.
> > > > > > > > + * @reserved2:		Reserved
> > > > > > >
> > > > > > > Reserved and must be 0?
> > > > > >
> > > > > > Not a must.
> > > > >
> > > > > That's guaranteed to come back and bite you in the end.
> > > >
> > > > OK. I can fill them with zero before passing them to hypervisor.
> > > >
> > > > > You all have read the "how to write a good api" document, right?
> > > >
> > > > Is it Documentation/driver-api/ioctl.rst? Or i missed..
> > >
> > > That's one good document, but no, not what I was referring to.  I was
> > > thinking of Documentation/process/adding-syscalls.rst, which is what you
> > > are doing here implicitly with these new ioctls (every ioctl is a brand
> > > new syscall.)
> >
> > I will read it as well. Thanks.
> >
> > >
> > > > > > > What are they reserved for?
> > > > > > >
> > > > > > > Same for all of the reserved fields, why?
> > > > > >
> > > > > > Some reserved fields are to map layout in the hypervisor side, others
> > > > > > are for future use.
> > > > >
> > > > > ioctls should not have these, again, please read the documentation.  If
> > > > > you need something new in the future, just make a new ioctl.
> > > >
> > > > OK. I will remove some reserved fields for scalability.
> > >
> > > "scalability" should have nothing to do with any of this, right?  What
> > > am I missing?
> >
> > Sorry, i meant reserved fields for future use.
>
> Again, this is not how you do that at all.  If you need something "in
> the future", create it then.  What you are doing here ensures that you
> will never be able to do it then either, so don't even pretend :)
>
> Read the syscall document for why this is the case.

Alright. I will remove that type of reserved fields. Thank you.

> > > > Though i can
> > > > keep some reserved fields for alignment (and to keep same data structure
> > > > layout with the hypervisor), right?
> > > > Documentation/driver-api/ioctl.rst says that explicit reserved fields
> > > > could be used.
> > >
> > > If you need alignment, yes, that is fine, but that's not what you are
> > > saying these are for.  And if you need alignment, why not move things
> > > around so they are properly aligned.
> > >
> > > And this structure has nothing to do with the hypervisor structure,
> > > that's a internal-kernel structure, not a userspace-visable thing if you
> > > are doing things correctly.
> >
> > It's the same structure with the one in hypervisor. HSM driver
> > doesn't maintain the VM much, it just pass the data for VM creation from
> > userspace to hypervisor.
>
> That sounds ripe for abuse, good luck!

The hypervisor will do the sanity check. In this case, HSM driver can be
kept simple.

Thanks
shuo