Re: RT Xen on ARM - R-Car series

[Andrii Anisov <andrii.anisov@gmail.com>]

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.

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel