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

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Message-ID: <5b2fa2b3-ca77-4d6e-a474-75c196b8fefc@redhat.com>
Date: Tue, 10 Sep 2024 12:33:04 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Adrian Hunter <adrian.hunter@...el.com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>, seanjc@...gle.com,
 kvm@...r.kernel.org
Cc: kai.huang@...el.com, dmatlack@...gle.com, isaku.yamahata@...il.com,
 yan.y.zhao@...el.com, nik.borisov@...e.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 20/21] KVM: TDX: Finalize VM initialization

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()).

Also, I think that in patch 16 (whether merged or not) nr_premapped 
should not be incremented, once kvm_tdx->finalized has been set?

Paolo