Re: [RFC PATCH v1 21/28] KVM: introduce KVM_SEV_ISSUE_CMD ioctl

[Paolo Bonzini <pbonzini@redhat.com>]

> > If I understanding correctly then you are recommending that instead of
> > exporting various functions from PSP drv we should expose one function
> > for the all the guest command handling (something like this).
> >
> > My understanding is that a user could exhaust the ASIDs for encrypted
> > VMs if it was allowed to start an arbitrary number of KVM guests.  So
> > we would need some kind of control.  Is this correct?
> 
> Yes, there is limited number of ASIDs for encrypted VMs. Do we need to
> pass the psp_fd into SEV_ISSUE_CMD ioctl or can we handle it from Qemu
> itself ? e.g when user asks to transition a guest into SEV-enabled mode
> then before calling LAUNCH_START Qemu tries to open /dev/psp device. If
> open() returns success then we know user has permission to communicate
> with PSP firmware.

No, this is a stateful mechanism and it's hard to implement.  Passing a
/dev/psp file descriptor is the simplest way to "prove" that you have
access to the device.

Thanks,

Paolo

> > If so, does /dev/psp provide any functionality that you believe is
> > dangerous for the KVM userspace (which runs in a very confined
> > environment)?  Is this functionality blocked through capability
> > checks?
> 
> I do not see /dev/psp providing anything which would be dangerous to KVM
> userspace. It should be safe to access /dev/psp into KVM userspace.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>