linux-kernel - Re: [PART2 PATCH v4 07/11] iommu/amd: Introduce amd_iommu_update

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Date:	Thu, 14 Jul 2016 16:33:02 +0700
From:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:	Radim Krčmář <rkrcmar@...hat.com>
CC:	<joro@...tes.org>, <pbonzini@...hat.com>,
	<alex.williamson@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <sherry.hurwitz@....com>
Subject: Re: [PART2 PATCH v4 07/11] iommu/amd: Introduce amd_iommu_update_ga()



On 7/14/16 16:13, Suravee Suthikulpanit wrote:
>>>    unsigned long flags;
>>> +    struct amd_iommu *iommu;
>>> +
>>> +    if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir))
>>> +        return 0;
>>> +
>>> +    for_each_iommu(iommu) {
>>> +        struct amd_ir_data *ir_data;
>>> +
>>> +        spin_lock_irqsave(&iommu->gatag_ir_hash_lock, flags);
>>> +
>>> +        /* Note:
>>> +         * We need to update all interrupt remapping table entries
>>> +         * for targeting the specified vcpu. Here, we use gatag
>>> +         * as a hash key and iterate through all entries in the bucket.
>>> +         */
>>> +        hash_for_each_possible(iommu->gatag_ir_hash, ir_data, hnode,
>>> +                       AMD_IOMMU_GATAG(vm_id, vcpu_id)) {
>>> +            struct irte_ga *irte = (struct irte_ga *) ir_data->entry;
>>
>> |>> (The ga_tag check is missing here too.)
>> |>
>> |> Here, the intention is to update all interrupt remapping entries in
>> the
>> |> bucket w/ the same GATAG (i.e. vm_id + vcpu_id), where GATAG =
>> |> AMD_IOMMU_GATAG(vm_id, vcpu_id).
>>
>> Which is why you need to check that
>>    AMD_IOMMU_GATAG(vm_id, vcpu_id) == entry->fields_vapic.ga_tag
>>
>> The hashing function can map two different vm_id + vcpu_id to the same
>> bucket and hash_for_each_possible() would return both of them, but only
>> one belongs to the VCPU that we want to update.
>>
>> (And shouldn't there be only one match?)
>
> Actually, with your suggestion above, the hask key would be (vm_id &
> 0x3FFFFF << 8)| (vcpu_id & 0xFF). So, it should be unique for each vcpu
> of each vm, or am I still missing something?

Ok, one scenario would be when SVM run out of the VM_ID and having to 
start re-using them. Since we want SVM to generate ga_tag and just pass 
into IOMMU driver for it to program the IRTE, we probably can make an 
assumption that SVM would make sure that ga_tag would not conflict for 
each vm_id/vcpu_id.

Thanks,
Suravee

Thanks,
Suravee