Re: [Xen-devel] [PATCH RFC V2 5/6] xen, libxc: Request page fault injection via libxc

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-07-11 at 19:06 +0100, Andrew Cooper wrote:
> On 11/07/14 16:43, Razvan Cojocaru wrote:
> > Added new XEN_DOMCTL_set_pagefault_info hypercall, used by libxc's
> > new xc_domain_set_pagefault_info() function to set per-domain page
> > fault injection information. All a call does is set per-domain info,
> > and nothing actually happens until VMENTRY time, and then only if
> > all conditions are met (the guest is in user mode, the set value
> > matches CR3, and there are no other pending traps).
> > This mechanism allows bringing in swapped-out pages for inspection.
> >
> > Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> 
> For the record, I still think this is a bad idea to be working against a
> guest OS paging algorithm, and I am uneasy about whether it is sensible
> to introduce abilities like that into the Xen API.

Indeed.

From the tools side the new libxc function is a correct wrapping of the
underlying hypercall, so if/when the hypervisor maintainers are happy
with the interface it's fine by me, with one minor comment.

> >  
> > +int xc_domain_set_pagefault_info(xc_interface *xch,
> > +                                 uint32_t domid,
> > +                                 xen_domctl_set_pagefault_info_t *info)
> > +{
> > +    DECLARE_DOMCTL;
> > +
> > +    if (info == NULL)
> > +        return -1;
> > +
> > +    domctl.cmd = XEN_DOMCTL_set_pagefault_info;
> > +    domctl.domain = (domid_t)domid;
> > +    domctl.u.set_pagefault_info.address_space = info->address_space;
> > +    domctl.u.set_pagefault_info.virtual_address = info->virtual_address;
> > +    domctl.u.set_pagefault_info.write_access = info->write_access;

Aren't these three lines just "domctl.u.set_pagefault_info = *info;"?

Ian.



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