Re: [Xen-devel] [PATCH RFC 2/4] x86/mem_access: mem_access and mem_event changes to support PV domains

["Aravindh Puthiyaparambil (aravindp)" <aravindp@xxxxxxxxx>]

>> @@ -65,12 +91,27 @@ int mem_access_memop(unsigned long cmd,
>>     case XENMEM_access_op_set_access:
>>     {
>>         unsigned long start_iter = cmd & ~MEMOP_CMD_MASK;
>> +        unsigned long pfn = mao.pfn;
>>
>>         rc = -EINVAL;
>> -        if ( (mao.pfn != ~0ull) &&
>> +        if ( !domain_valid_for_mem_access(d) )
>> +            break;
>> +
>> +        if ( unlikely(is_pv_domain(d)  && pfn != ~0ull) )
>> +            pfn = get_gpfn_from_mfn(mao.pfn);
>> +
>> +        /*
>> +         * max_pfn for PV domains is obtained from the shared_info
>> + structures
>Another one of my potentially inaccurate attempts to help:
>
>I don't know that you need to care about pfn here. This is a PV domain, so a
>page may be "hung" from it without requiring a specific translation to a slot 
>in
>the physmap. There are precedents for this, e.g. the shared info page, the
>grant table pages.
>
>In other words, you could make the men event ring page a xen page, share it
>with the guest so it becomes mappable (share_xen_page_with_guest), and
>then xc_map in dom0 libxc would be happily able to map it. With no need to
>worry ever about finding a pfn in the guest domain for this page.
>
>Of course you'll need to keep track of this page and properly dispose of it
>regardless.

OK, I think this is what I am doing as seen below.

Thanks,
Aravindh

>> +    case XENMEM_access_op_create_ring_page:
>> +    {
>> +        void *access_ring_va;
>> +
>> +        /*
>> +         * mem_access listeners for HVM domains need not call
>> +         * xc_mem_access_set_ring_pfn() as the special ring page would have
>been
>> +         * setup during domain creation.
>> +         */
>> +        rc = -ENOSYS;
>> +        if ( is_hvm_domain(d) )
>> +            break;
>> +
>> +        /*
>> +         * The ring page was created by a mem_access listener but was not
>> +         * freed. Do not allow another xenheap page to be allocated.
>> +         */
>> +        if ( mfn_valid(d->arch.pv_domain.access_ring_mfn) )
>> +        {
>> +            rc = -EPERM;
>> +            break;
>> +        }
>> +
>> +        access_ring_va = alloc_xenheap_page();
>> +        if ( access_ring_va == NULL )
>> +        {
>> +            rc = -ENOMEM;
>> +            break;
>> +        }
>> +
>> +        clear_page(access_ring_va);
>> +        share_xen_page_with_guest(virt_to_page(access_ring_va), d,
>> +                                  XENSHARE_writable);
>> +
>> +        d->arch.pv_domain.access_ring_mfn =
>> + _mfn(virt_to_mfn(access_ring_va));
>> +
>> +        rc = 0;
>> +        break;
>> +    }
>> @@ -123,6 +236,21 @@ int mem_access_send_req(struct domain *d,
>mem_event_request_t *req)
>>     return 0;
>> }
>>
>> +/* Free the xenheap page used for the PV access ring */ void
>> +mem_access_free_pv_ring(struct domain *d) {
>> +    struct page_info *pg =
>> +mfn_to_page(d->arch.pv_domain.access_ring_mfn);
>> +
>> +    if ( !mfn_valid(d->arch.pv_domain.access_ring_mfn) )
>> +        return;
>> +
>> +    BUG_ON(page_get_owner(pg) != d);
>> +    if ( test_and_clear_bit(_PGC_allocated, &pg->count_info) )
>> +        put_page(pg);
>> +    free_xenheap_page(mfn_to_virt(mfn_x(d-
>>arch.pv_domain.access_ring_mfn)));
>> +    d->arch.pv_domain.access_ring_mfn = _mfn(INVALID_MFN); }
>> +

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