Re: [PATCH V2] KVM: SEV: Acquire vcpu mutex when updating VMSA

[Paolo Bonzini <pbonzini@redhat.com>]

On 15/09/21 19:17, Peter Gonda wrote:
> Adds vcpu mutex guard to the VMSA updating code. Refactors out
> __sev_launch_update_vmsa() function to deal with per vCPU parts
> of sev_launch_update_vmsa().
> 
> Fixes: ad73109ae7ec ("KVM: SVM: Provide support to launch and run an SEV-ES guest")
> 
> Signed-off-by: Peter Gonda <pgonda@google.com>
> Cc: Marc Orr <marcorr@google.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Sean Christopherson <seanjc@google.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Cc: kvm@vger.kernel.org
> Cc: stable@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> ---
> 
> V2
>   * Refactor per vcpu work to separate function.
>   * Remove check to skip already initialized VMSAs.
>   * Removed vmsa struct zeroing.
> 
> ---
>   arch/x86/kvm/svm/sev.c | 53 ++++++++++++++++++++++++------------------
>   1 file changed, 30 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 75e0b21ad07c..766510fe3abb 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -595,43 +595,50 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm)
>   	return 0;
>   }
>   
> -static int sev_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +static int __sev_launch_update_vmsa(struct kvm *kvm, struct kvm_vcpu *vcpu,
> +				    int *error)
>   {
> -	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>   	struct sev_data_launch_update_vmsa vmsa;
> +	struct vcpu_svm *svm = to_svm(vcpu);
> +	int ret;
> +
> +	/* Perform some pre-encryption checks against the VMSA */
> +	ret = sev_es_sync_vmsa(svm);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * The LAUNCH_UPDATE_VMSA command will perform in-place encryption of
> +	 * the VMSA memory content (i.e it will write the same memory region
> +	 * with the guest's key), so invalidate it first.
> +	 */
> +	clflush_cache_range(svm->vmsa, PAGE_SIZE);
> +
> +	vmsa.reserved = 0;
> +	vmsa.handle = to_kvm_svm(kvm)->sev_info.handle;
> +	vmsa.address = __sme_pa(svm->vmsa);
> +	vmsa.len = PAGE_SIZE;
> +	return sev_issue_cmd(kvm, SEV_CMD_LAUNCH_UPDATE_VMSA, &vmsa, error);
> +}
> +
> +static int sev_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
>   	struct kvm_vcpu *vcpu;
>   	int i, ret;
>   
>   	if (!sev_es_guest(kvm))
>   		return -ENOTTY;
>   
> -	vmsa.reserved = 0;
> -
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		struct vcpu_svm *svm = to_svm(vcpu);
> -
> -		/* Perform some pre-encryption checks against the VMSA */
> -		ret = sev_es_sync_vmsa(svm);
> +	kvm_for_each_vcpu(i, vcpu, kvm) {
> +		ret = mutex_lock_killable(&vcpu->mutex);
>   		if (ret)
>   			return ret;
>   
> -		/*
> -		 * The LAUNCH_UPDATE_VMSA command will perform in-place
> -		 * encryption of the VMSA memory content (i.e it will write
> -		 * the same memory region with the guest's key), so invalidate
> -		 * it first.
> -		 */
> -		clflush_cache_range(svm->vmsa, PAGE_SIZE);
> +		ret = __sev_launch_update_vmsa(kvm, vcpu, &argp->error);
>   
> -		vmsa.handle = sev->handle;
> -		vmsa.address = __sme_pa(svm->vmsa);
> -		vmsa.len = PAGE_SIZE;
> -		ret = sev_issue_cmd(kvm, SEV_CMD_LAUNCH_UPDATE_VMSA, &vmsa,
> -				    &argp->error);
> +		mutex_unlock(&vcpu->mutex);
>   		if (ret)
>   			return ret;
> -
> -		svm->vcpu.arch.guest_state_protected = true;
>   	}
>   
>   	return 0;
> 

Queued, thanks.

Paolo