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Subject: Re: [PATCH] iommu/amd: fix interrupt remapping for avic
To:     Maxim Levitsky <mlevitsk@redhat.com>, linux-kernel@vger.kernel.org
Cc:     "open list:AMD IOMMU (AMD-VI)" <iommu@lists.linux-foundation.org>,
        Joao Martins <joao.m.martins@oracle.com>,
        Joerg Roedel <joro@8bytes.org>,
        "Grimm, Jon" <jon.grimm@amd.com>
References: <20200913124211.6419-1-mlevitsk@redhat.com>
 <60856c61-062b-8d92-e565-38bd00855228@amd.com>
 <04a8ab5cb1f6662f72bcad856da3415d6d9b2593.camel@redhat.com>
From:   Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
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On 9/15/20 6:25 PM, Maxim Levitsky wrote:
> On Mon, 2020-09-14 at 21:48 +0700, Suravee Suthikulpanit wrote:
>> Maxim,
>>
>> On 9/13/2020 7:42 PM, Maxim Levitsky wrote:
>>> Commit e52d58d54a32 ("iommu/amd: Use cmpxchg_double() when updating 128-bit IRTE")
>>> accidentally removed an assumption that modify_irte_ga always set the valid bit
>>> and amd_iommu_activate_guest_mode relied on that.
>>>
>>> Side effect of this is that on my machine, VFIO based VMs with AVIC enabled
>>> would eventually crash and show IOMMU errors like that:
>>>
>>> AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0055 address=0xfffffffdf8000000 flags=0x0008]
>>>
>>> Fixes: e52d58d54a321 ("iommu/amd: Use cmpxchg_double() when updating 128-bit IRTE")
>>> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
>>> ---
>>>    drivers/iommu/amd/iommu.c | 1 +
>>>    1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
>>> index 07ae8b93887e5..aff4cc1869356 100644
>>> --- a/drivers/iommu/amd/iommu.c
>>> +++ b/drivers/iommu/amd/iommu.c
>>> @@ -3853,6 +3853,7 @@ int amd_iommu_activate_guest_mode(void *data)
>>>    	entry->hi.fields.ga_root_ptr       = ir_data->ga_root_ptr;
>>>    	entry->hi.fields.vector            = ir_data->ga_vector;
>>>    	entry->lo.fields_vapic.ga_tag      = ir_data->ga_tag;
>>> +	entry->lo.fields_remap.valid = 1;
>>>    
>>>    	return modify_irte_ga(ir_data->irq_2_irte.devid,
>>>    			      ir_data->irq_2_irte.index, entry, ir_data);
>>>
>>
>> Could you please try with the following patch instead?
>>
>> --- a/drivers/iommu/amd/iommu.c
>> +++ b/drivers/iommu/amd/iommu.c
>> @@ -3840,14 +3840,18 @@ int amd_iommu_activate_guest_mode(void *data)
>>    {
>>           struct amd_ir_data *ir_data = (struct amd_ir_data *)data;
>>           struct irte_ga *entry = (struct irte_ga *) ir_data->entry;
>> +       u64 valid;
>>
>>           if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) ||
>>               !entry || entry->lo.fields_vapic.guest_mode)
>>                   return 0;
>>
>> +       valid = entry->lo.fields_vapic.valid;
>> +
>>           entry->lo.val = 0;
>>           entry->hi.val = 0;
>>
>> +       entry->lo.fields_vapic.valid       = valid;
>>           entry->lo.fields_vapic.guest_mode  = 1;
>>           entry->lo.fields_vapic.ga_log_intr = 1;
>>           entry->hi.fields.ga_root_ptr       = ir_data->ga_root_ptr;
>> @@ -3864,12 +3868,14 @@ int amd_iommu_deactivate_guest_mode(void *data)
>>           struct amd_ir_data *ir_data = (struct amd_ir_data *)data;
>>           struct irte_ga *entry = (struct irte_ga *) ir_data->entry;
>>           struct irq_cfg *cfg = ir_data->cfg;
>> -       u64 valid = entry->lo.fields_remap.valid;
>> +       u64 valid;
>>
>>           if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) ||
>>               !entry || !entry->lo.fields_vapic.guest_mode)
>>                   return 0;
>>
>> +       valid = entry->lo.fields_remap.valid;
>> +
>>           entry->lo.val = 0;
>>           entry->hi.val = 0;
> I see. I based my approach on the fact that valid bit was
> set always to true anyway before, plus that amd_iommu_activate_guest_mode
> should be really only called when someone activates a valid interrupt remapping
> entry, but IMHO the approach of preserving the valid bit is safer anyway.
> 
> It works on my system (I applied the patch manually, since either your or my email client,
> seems to mangle the patch)
> 
> Thanks,
> Best regards,
> 	Maxim Levitsky
> 
> 

Sorry for the mangled patch. I'll submit the patch w/ your information. Thanks for your help reporting, debugging, and 
testing the patch.

Sincerely,

Suravee
>> --
> 
>>
>> Thanks,
>> Suravee
>>
> 
>