Re: [Xen-devel] [PATCH v14 06/11] x86/hvm/ioreq: add a new mappable resource type...

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.12.17 at 10:51, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: Paul Durrant [mailto:paul.durrant@xxxxxxxxxx]
>> Sent: 28 November 2017 15:09
>> +static int hvm_alloc_ioreq_mfn(struct hvm_ioreq_server *s, bool buf)
>> +{
>> +    struct domain *currd = current->domain;
>> +    struct hvm_ioreq_page *iorp = buf ? &s->bufioreq : &s->ioreq;
>> +
>> +    if ( iorp->page )
>> +    {
>> +        /*
>> +         * If a guest frame has already been mapped (which may happen
>> +         * on demand if hvm_get_ioreq_server_info() is called), then
>> +         * allocating a page is not permitted.
>> +         */
>> +        if ( !gfn_eq(iorp->gfn, INVALID_GFN) )
>> +            return -EPERM;
>> +
>> +        return 0;
>> +    }
>> +
>> +    /*
>> +     * Allocated IOREQ server pages are assigned to the emulating
>> +     * domain, not the target domain. This is because the emulator is
>> +     * likely to be destroyed after the target domain has been torn
>> +     * down, and we must use MEMF_no_refcount otherwise page allocation
>> +     * could fail if the emulating domain has already reached its
>> +     * maximum allocation.
>> +     */
>> +    iorp->page = alloc_domheap_page(currd, MEMF_no_refcount);
> 
> This is no longer going to work as it is predicated on my original 
> modification to HYPERVISOR_mmu_update (which allowed a PV domain to map a 
> foreign MFN from a domain over which it had privilege as if the MFN was 
> local). Because that mechanism was decided against, this code needs to change 
> to use the target domain of the ioreq server rather than the calling domain. 
> I will verfy this modification and submit v15 of the series.
> 
> Jan, are you ok for me to keep your R-b?

This is all pretty fragile - better drop it and I'll then take a look
once you've sent the new version.

Jan


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