Re: [Xen-devel] [PATCH V2 25/25] x86/vvtd: save and restore emulated VT-d

[Chao Gao <chao.gao@xxxxxxxxx>]

On Wed, Aug 23, 2017 at 01:19:41PM +0100, Roger Pau Monné wrote:
>On Wed, Aug 09, 2017 at 04:34:26PM -0400, Lan Tianyu wrote:
>> From: Chao Gao <chao.gao@xxxxxxxxx>
>> 
>> Wrap some useful status in a new structure hvm_hw_vvtd, following
>> the customs of vlapic, vioapic and etc. Provide two save-restore
>> pairs to save/restore registers and non-register status.
>> 
>> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
>> Signed-off-by: Lan Tianyu <tianyu.lan@xxxxxxxxx>
>> ---
>> diff --git a/xen/include/public/arch-x86/hvm/save.h 
>> b/xen/include/public/arch-x86/hvm/save.h
>> index fd7bf3f..10536cb 100644
>> --- a/xen/include/public/arch-x86/hvm/save.h
>> +++ b/xen/include/public/arch-x86/hvm/save.h
>> @@ -639,10 +639,32 @@ struct hvm_msr {
>>  
>>  #define CPU_MSR_CODE  20
>>  
>> +struct hvm_hw_vvtd_regs {
>> +    uint8_t data[1024];
>> +};
>> +
>> +DECLARE_HVM_SAVE_TYPE(IOMMU_REGS, 21, struct hvm_hw_vvtd_regs);
>> +
>> +struct hvm_hw_vvtd
>> +{
>> +    /* VIOMMU_STATUS_XXX */
>> +    uint32_t status;
>> +    /* Fault Recording index */
>> +    uint32_t frcd_idx;
>> +    /* Is in Extended Interrupt Mode? */
>> +    uint32_t eim;
>> +    /* Max remapping entries in IRT */
>> +    uint32_t irt_max_entry;
>> +    /* Interrupt remapping table base gfn */
>> +    uint64_t irt;
>> +};
>> +
>> +DECLARE_HVM_SAVE_TYPE(IOMMU, 22, struct hvm_hw_vvtd);
>
>Why two separate structures? It should be the same structure.

Hi, Roger.

Thank you for your review. I agree with most of your comments on the
whole series. I will only reply to some points I think still need
discussion.

Here we use two separate structures for some field cannot be infered
from the struct hvm_hw_vvtd_regs. For example, the 'irt' is the gfn of
the base address Interrupt Remapping Table. The field is set through
1. set the register DMAR_IRTE_REG in hvm_hw_vvtd_regs.
2. send a command to vtd by writting another command register.

If the current base address is A, and guest wants to update the base
address to B and finish the first step. Unfortunately, saving and
restoring happen here. In this case, we need the struct hvm_hw_vvtd
to correctly restore some information.

Thanks
Chao

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