Re: [PATCH v5 5/7] xen/arm: Add XEN_DOMCTL_dt_overlay and device attachment to domains

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 24 May 2024, Julien Grall wrote:
> Hi Stefano,
> 
> On 24/05/2024 03:18, Stefano Stabellini wrote:
> > From: Henry Wang <xin.wang2@xxxxxxx>
> > 
> > In order to support the dynamic dtbo device assignment to a running
> > VM, the add/remove of the DT overlay and the attach/detach of the
> > device from the DT overlay should happen separately. Therefore,
> > repurpose the existing XEN_SYSCTL_dt_overlay to only add the DT
> > overlay to Xen device tree, instead of assigning the device to the
> > hardware domain at the same time. It is OK to change the sysctl behavior
> > as this feature is experimental so changing sysctl behavior and breaking
> > compatibility is OK.
> > 
> > Add the XEN_DOMCTL_dt_overlay with operations
> > XEN_DOMCTL_DT_OVERLAY_ATTACH to do the device assignment to the domain.
> > 
> > The hypervisor firstly checks the DT overlay passed from the toolstack
> > is valid. Then the device nodes are retrieved from the overlay tracker
> > based on the DT overlay. The attach of the device is implemented by
> > mapping the IRQ and IOMMU resources. All devices in the overlay are
> > assigned to a single domain.
> > 
> > Also take the opportunity to make one coding style fix in sysctl.h.
> > 
> > xen,reg is to be used to handle non-1:1 mappings but it is currently
> > unsupported.
> 
> This means that we would still try to use 1:1 mappings for non-directmap
> domain. Given that the overlay is a blob, I am a bit concerned that the user
> may not notice any clash and it would be difficult to debug.
> 
> Therefore, I would like xen,reg to be mandatory when using non directmapped
> domain. For now, the best approach would be to prevent device assignment if
> !is_domain_direct_mapped().

That's fine, I'll make the change


> > +long dt_overlay_domctl(struct domain *d, struct xen_domctl_dt_overlay *op)
> > +{
> > +    long ret;
> > +    void *overlay_fdt;
> > +
> > +    if ( op->overlay_op != XEN_DOMCTL_DT_OVERLAY_ATTACH )
> > +        return -EOPNOTSUPP;
> > +
> > +    if ( op->overlay_fdt_size == 0 || op->overlay_fdt_size > KB(500) )
> 
> Please add #define DT_OVERLAY_MAX_SIZE KB(500) and use it here and the other
> place.

OK