linux-kernel - Re: [PATCH 1/3 V3] KVM, SEV: Refactor out function for unregistering encrypted regions

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Date:   Thu, 29 Jul 2021 21:17:16 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Gonda <pgonda@...gle.com>
Cc:     kvm@...r.kernel.org, Brijesh Singh <brijesh.singh@....com>,
        Marc Orr <marcorr@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3 V3] KVM, SEV: Refactor out function for unregistering
 encrypted regions

Prefer "KVM: SVM:" or "KVM: SEV:" in the shortlog, i.e. colon instead of comma
after KVM.

On Mon, Jul 26, 2021, Peter Gonda wrote:
> Factor out helper function for freeing the encrypted region list.
> 
> Signed-off-by: Peter Gonda <pgonda@...gle.com>
> Reviewed-by: Brijesh Singh <brijesh.singh@....com>
> Reviewed-by: Marc Orr <marcorr@...gle.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Dr. David Alan Gilbert <dgilbert@...hat.com>
> Cc: Brijesh Singh <brijesh.singh@....com>
> Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
> Cc: Wanpeng Li <wanpengli@...cent.com>
> Cc: Jim Mattson <jmattson@...gle.com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  arch/x86/kvm/svm/sev.c | 26 +++++++++++++++++---------
>  1 file changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index b59c464bcdfa..6cb61d36fd5e 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1775,11 +1775,25 @@ int svm_vm_copy_asid_from(struct kvm *kvm, unsigned int source_fd)
>  	return ret;
>  }
>  
> +static void unregister_enc_regions(struct kvm *kvm,
> +					    struct list_head *mem_regions)

Indentation is wonky.  There's an extra tab and an extra space.

> +{
> +	struct enc_region *pos, *q;
> +
> +	lockdep_assert_held(&kvm->lock);
> +
> +	if (list_empty(mem_regions))
> +		return;
> +
> +	list_for_each_entry_safe(pos, q, mem_regions, list) {
> +		__unregister_enc_region_locked(kvm, pos);
> +		cond_resched();
> +	}
> +}
> +
>  void sev_vm_destroy(struct kvm *kvm)
>  {
>  	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> -	struct list_head *head = &sev->regions_list;
> -	struct list_head *pos, *q;
>  
>  	if (!sev_guest(kvm))
>  		return;
> @@ -1803,13 +1817,7 @@ void sev_vm_destroy(struct kvm *kvm)
>  	 * if userspace was terminated before unregistering the memory regions
>  	 * then lets unpin all the registered memory.
>  	 */
> -	if (!list_empty(head)) {
> -		list_for_each_safe(pos, q, head) {
> -			__unregister_enc_region_locked(kvm,
> -				list_entry(pos, struct enc_region, list));
> -			cond_resched();
> -		}
> -	}
> +	unregister_enc_regions(kvm, &sev->regions_list);
>  
>  	mutex_unlock(&kvm->lock);

Is there any reason for taking kvm->lock in this path?  The VM is being destroyed,
there should be no other references, i.e. this is the only task that can be doing
anything with @kvm.

The lock is harmless, it just always gives me pause to see the cond_resched()
while holding kvm->lock.

> -- 
> 2.32.0.432.gabb21c7263-goog
>