On 24.06.2020 14:47, Julien Grall wrote: > Hi, > > On 24/06/2020 13:08, Jan Beulich wrote: >> On 24.06.2020 12:52, Julien Grall wrote: >>> Hi Jan, >>> >>> On 24/06/2020 11:05, Jan Beulich wrote: >>>> On 23.06.2020 19:32, Roger Pau Monné wrote: >>>>> On Tue, Jun 23, 2020 at 05:04:53PM +0200, Jan Beulich wrote: >>>>>> On 23.06.2020 15:52, Roger Pau Monne wrote: >>>>>>> XENMEM_acquire_resource and it's related structure is currently inside >>>>>>> a __XEN__ or __XEN_TOOLS__ guarded section to limit it's scope to the >>>>>>> hypervisor or the toolstack only. This is wrong as the hypercall is >>>>>>> already being used by the Linux kernel at least, and as such needs to >>>>>>> be public. >>>>>> >>>>>> Actually - how does this work for the Linux kernel, seeing >>>>>> >>>>>> rc = rcu_lock_remote_domain_by_id(xmar.domid, &d); >>>>>> if ( rc ) >>>>>> return rc; >>>>>> >>>>>> rc = xsm_domain_resource_map(XSM_DM_PRIV, d); >>>>>> if ( rc ) >>>>>> goto out; >>>>>> >>>>>> in the function? >>>>> >>>>> It's my understanding (I haven't tried to use that hypercall yet on >>>>> FreeBSD, so I cannot say I've tested it), that xmar.domid is the >>>>> remote domain, which the functions locks and then uses >>>>> xsm_domain_resource_map to check whether the current domain has >>>>> permissions to do privileged operations against it. >>>> >>>> Yes, but that's a tool stack operation, not something the kernel >>>> would do all by itself. The kernel would only ever pass DOMID_SELF >>>> (or the actual local domain ID), I would think. >>> >>> You can't issue that hypercall directly from userspace because you need >>> to map the page in the physical address space of the toolstack domain. >>> >>> So the kernel has to act as the proxy for the hypercall. This is >>> implemented as mmap() in Linux. >> >> Oh, and there's no generic wrapping available here, unlike for >> dmop. > > It is not clear to me the sort of generic wrapping you are referring to. > Are you referring to a stable interface for an application? > >> Makes me wonder whether, for this purpose, there should >> be (have been) a new dmop with identical functionality, to >> allow such funneling. > > I am not sure how using DMOP will allow us to implement it fully in > userspace. Do you mind expanding it?
dmop was designed so that a kernel proxying requests wouldn't need updating for every new request added to the interface. If the request here was made through a new dmop, the kernel would never have had a need to know of an interface structure that's of no interest to it, but only to the tool stack. Jan
