Re: [PATCH 20/21] KVM: TDX: Finalize VM initialization

[Adrian Hunter]

On 10/09/24 14:15, Adrian Hunter wrote:
> On 10/09/24 13:33, Paolo Bonzini wrote:
>> On 9/4/24 17:37, Adrian Hunter wrote:
>>> Isaku was going to lock the mmu.  Seems like the change got lost.
>>> To protect against racing with KVM_PRE_FAULT_MEMORY,
>>> KVM_TDX_INIT_MEM_REGION, tdx_sept_set_private_spte() etc
>>> e.g. Rename tdx_td_finalizemr to __tdx_td_finalizemr and add:
>>>
>>> static int tdx_td_finalizemr(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
>>> {
>>>     int ret;
>>>
>>>     write_lock(&kvm->mmu_lock);
>>>     ret = __tdx_td_finalizemr(kvm, cmd);
>>>     write_unlock(&kvm->mmu_lock);
>>>
>>>     return ret;
>>> }
>>
>> kvm->slots_lock is better.  In tdx_vcpu_init_mem_region() you can take it before the is_td_finalized() so that there is a lock that is clearly protecting kvm_tdx->finalized between the two.  (I also suggest switching to guard() in tdx_vcpu_init_mem_region()).
> 
> Doesn't KVM_PRE_FAULT_MEMORY also need to be protected?

Ah, but not if pre_fault_allowed is false.

> 
>>
>> Also, I think that in patch 16 (whether merged or not) nr_premapped should not be incremented, once kvm_tdx->finalized has been set?
> 
> tdx_sept_set_private_spte() checks is_td_finalized() to decide
> whether to call tdx_mem_page_aug() or tdx_mem_page_record_premap_cnt()
> Refer patch 14 "KVM: TDX: Implement hooks to propagate changes
> of TDP MMU mirror page table" for the addition of
> tdx_sept_set_private_spte()
> 
>