Re: [Xen-devel] [PATCH v3 07/15] argo: implement the register op

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Sun, Jan 06, 2019 at 11:42:40PM -0800, Christopher Clark wrote:
> The register op is used by a domain to register a region of memory for
> receiving messages from either a specified other domain, or, if specifying a
> wildcard, any domain.
> 
> This operation creates a mapping within Xen's private address space that
> will remain resident for the lifetime of the ring. In subsequent commits,
> the hypervisor will use this mapping to copy data from a sending domain into
> this registered ring, making it accessible to the domain that registered the
> ring to receive data.
> 
> Wildcard any-sender rings are default disabled and registration will be
> refused with EPERM unless they have been specifically enabled with the
> argo-mac boot option introduced here. The reason why the default for
> wildcard rings is 'deny' is that there is currently no means to protect the
> ring from DoS by a noisy domain spamming the ring, affecting other domains
> ability to send to it. This will be addressed with XSM policy controls in
> subsequent work.
> 
> Since denying access to any-sender rings is a significant functional
> constraint, a new bootparam is provided to enable overriding this:
>  "argo-mac" variable has allowed values: 'permissive' and 'enforcing'.
> Even though this is a boolean variable, use these descriptive strings in
> order to make it obvious to an administrator that this has potential
> security impact.
> 
> The p2m type of the memory supplied by the guest for the ring must be
> p2m_ram_rw and the memory will be pinned as PGT_writable_page while the ring
> is registered.
> 
> xen_argo_page_descr_t type is introduced as a page descriptor, to convey
> both the physical address of the start of the page and its granularity. The
> smallest granularity page is assumed to be 4096 bytes and the lower twelve
> bits of the type are used to indicate the size of page of memory supplied.
> The implementation of the hypercall op currently only supports 4K pages.
> 

What is the resolution for the Arm issues mentioned by Julien? I read
the conversation in previous thread. A solution seemed to have been
agreed upon, but the changelog doesn't say anything about it.

Wei.

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