Re: [Qemu-devel] [PULL v5 29/57] intel_iommu: add SID validation for IR

[Jan Kiszka]

On 2016-08-02 10:36, Peter Xu wrote:
> On Mon, Aug 01, 2016 at 06:39:05PM +0200, Jan Kiszka wrote:
> 
> [...]
> 
>>>  static MemTxResult vtd_mem_ir_read(void *opaque, hwaddr addr,
>>> @@ -2209,11 +2250,17 @@ static MemTxResult vtd_mem_ir_write(void *opaque, 
>>> hwaddr addr,
>>>  {
>>>      int ret = 0;
>>>      MSIMessage from = {}, to = {};
>>> +    uint16_t sid = X86_IOMMU_SID_INVALID;
>>>  
>>>      from.address = (uint64_t) addr + VTD_INTERRUPT_ADDR_FIRST;
>>>      from.data = (uint32_t) value;
>>>  
>>> -    ret = vtd_interrupt_remap_msi(opaque, &from, &to);
>>> +    if (!attrs.unspecified) {
>>> +        /* We have explicit Source ID */
>>> +        sid = attrs.requester_id;
>>> +    }
>>
>> ...here you fall back to X86_IOMMU_SID_INVALID if writer to this region
>> has not provided some valid attrs. That is questionable, defeats
>> validation of the IOAPIC e.g. (and you can see lots of
>> X86_IOMMU_SID_INVALID in vtd_irte_get when booting a guest).
>>
>> The credits also go to David who noticed that he still doesn't get a
>> proper ID from the IOAPIC while implementing AMD IR. Looks like we need
>> to enlighten the IOAPIC MSI writes...
> 
> Jan, David,
> 
> At the time when drafting the patch, I skipped SID verification for
> IOAPIC interrupts since it differs from generic PCI devices (no
> natural requester ID, so need some hacky lines to enable it).

It's not hacky at all if done properly. For Intel it is simply
(Q35_PSEUDO_BUS_PLATFORM << 8) | Q35_PSEUDO_DEVFN_IOAPIC, but it will be
0x00a0 (as constant as well) for AMD. So we need some interface to tell
those parameters to the IOMMU. Keep in mind that we will need a similar
interface for other platform devices, e.g. the HPET.

> 
> I can try to cook another seperate patch to enable it (for 2.8
> possibly?). Thanks for pointing out this issue.

David needs that IOAPIC ID as well in order to finish interrupt
remapping on AMD. Please synchronize with him who will implement what.

Jan

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