Re: [PATCH V1 3/6] xen/virtio: Add option to restrict memory access under Xen

[Borislav Petkov <bp@xxxxxxxxx>]

On Tue, Apr 26, 2022 at 07:16:16AM +0200, Juergen Gross wrote:
> Christoph suggested (rather firmly) this would be the way to go.

Yeah, I saw it but I don't think it is the right way to go.

What happens the next time a guest needs to query the platform
underneath? Misuse these interfaces again?

Because people will see the Xen use and say, hey, look, I will use this
for my funky HV too.

Even worse: what happens if Xen decides to implement SEV/TDX? Then
you're in for a world of fun.

Now, if we want to *extend* the interfaces to have something as generic
as, say, platform_has() and that should be the way for generic kernel
code running in the guest to query the platform capabilities, then sure,
by all means.

> This is needed on guest side at a rather hypervisor independent place.
> 
> So a capability of some sort seems appropriate.
> 
> Another suggestion of mine was to have a callback (or flag) in
> struct x86_hyper_runtime for that purpose.

This becomes an issue if the HV is not x86 - then you need a different
method of querying it, which then underneath will call the arch-specific
interface.

I don't know how much of querying guests need to do and how they've been
doing that so far. Depending on the requirements, we probably should
think about a clean design from the get-go instead of homegrown things.

Thx.

-- 
Regards/Gruss,
    Boris.

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