linux-kernel - Re: [PATCH v3 13/16] powerpc/pseries/iommu: Don't use dma_iommu

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Date:   Tue, 6 Aug 2019 07:48:41 +0200
From:   Christoph Hellwig <hch@....de>
To:     Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Anshuman Khandual <anshuman.linux@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Hellwig <hch@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mike Anderson <andmike@...ux.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Ram Pai <linuxram@...ibm.com>,
        Claudio Carvalho <cclaudio@...ux.ibm.com>
Subject: Re: [PATCH v3 13/16] powerpc/pseries/iommu: Don't use
 dma_iommu_ops on secure guests

On Tue, Aug 06, 2019 at 02:22:34AM -0300, Thiago Jung Bauermann wrote:
> @@ -1318,7 +1319,10 @@ void iommu_init_early_pSeries(void)
>  	of_reconfig_notifier_register(&iommu_reconfig_nb);
>  	register_memory_notifier(&iommu_mem_nb);
>  
> -	set_pci_dma_ops(&dma_iommu_ops);
> +	if (is_secure_guest())
> +		set_pci_dma_ops(NULL);
> +	else
> +		set_pci_dma_ops(&dma_iommu_ops);

Shoudn't:

	if (!is_secure_guest())
		set_pci_dma_ops(&dma_iommu_ops);

be enough here, given that NULL is the default?

Also either way I think this conditional needs a comment explaining
why it is there.