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

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

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 :). Hopefully, no guest is modifying the mapping 
(i.e the virtual address point to a different physical address) afterwards.
> 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.

> +        if ( t != p2m_ram_rw || mfn_eq(v->runstate_mfn[i], INVALID_MFN) )
> +            return -EFAULT;
> +
> +        pg = mfn_to_page(v->runstate_mfn[i]);
> +        if ( !pg || !get_page_type(pg, PGT_writable_page) )
> +        {
> +            put_gfn(d, gfn_x(gfn));
> +            return -EFAULT;
> +        }
> +
> +        put_gfn(d, gfn_x(gfn));
> +
> +        if ( PFN_DOWN(gfn_x(gfn) + size) == PFN_DOWN(gfn_x(gfn)) )
This looks wrong, you seem to mix address and frame. I think you might want:

if ( gfn_eq(gfn_add(gfn, PFN_DOWN(size)), gfn) )

Cheers,

--
Julien Grall

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