Re: [Xen-devel] RT Xen on ARM - R-Car series

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

Hello,

On 01.02.19 19:40, Julien Grall wrote:
> On 01/02/2019 16:53, Roger Pau Monné wrote:
> > On Thu, Jan 31, 2019 at 11:14:37PM +0000, Julien Grall wrote:
> > > On 1/31/19 9:56 PM, Stefano Stabellini wrote:
> > > > On Thu, 31 Jan 2019, Julien Grall wrote:
> > > > > On 31/01/2019 12:00, Andrii Anisov wrote:
> > > > > > On 31.01.19 13:37, Julien Grall wrote:
> > So, I've got a hacky patch to 'fix' this on x86, by taking a reference
> > to the mfn behind the virtual address provided when setting up the
> > hypercall and mapping it in Xen.
> That was the idea I had in mind :). 
Looks interesting.

> Hopefully, no guest is modifying the mapping (i.e the virtual address point to 
> a different physical address) afterwards.
I guess, that mapping should not be moved around. Otherwise it would be broken 
even with the current implementation.
Moreover, having that buffer mapped to XEN will reduce context switch time as a 
side effect.

> > This however doesn't work on ARM due
> > to the lack of paging_gva_to_gfn. I guess there's something similar to
> > translate a guest virtual address into a gfn or a mfn?
> get_page_from_gva should to the job for you.
> > +int map_runstate_area(struct vcpu *v,
> > +                      struct vcpu_register_runstate_memory_area *area)
> > +{
> > +    unsigned long offset;
> > +    unsigned int i;
> > +    struct domain *d = v->domain;
> > +    size_t size =
> > +#ifdef CONFIG_COMPAT
> > +        has_32bit_shinfo((v)->domain) ? sizeof(*v->compat_runstate_guest) :
> > +#endif
> > +                                        sizeof(*v->runstate_guest);
> > +
> > +    if ( v->runstate_guest )
> > +    {
> > +        ASSERT_UNREACHABLE();
> > +        return -EBUSY;
> > +    }
> > +
> > +    offset = area->addr.p & ~PAGE_MASK;
> > +
> > +    for ( i = 0; i < ARRAY_SIZE(v->runstate_mfn); i++ )
> > +    {
> > +        p2m_type_t t;
> > +        uint32_t pfec = PFEC_page_present;
> > +        gfn_t gfn = _gfn(paging_gva_to_gfn(v, area->addr.p, &pfec));
> > +        struct page_info *pg;
> > +
> > +        if ( gfn_eq(gfn, INVALID_GFN) )
> > +            return -EFAULT;
> > +
> > +        v->runstate_mfn[i] = get_gfn(d, gfn_x(gfn), &t);
> get_gfn would need to be implemented on Arm.
I'm going to step into this, tomorrow I guess. I have to finish smth today.

--
Sincerely,
Andrii Anisov.

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