linux-kernel - Re: [PATCH RFC v1 6/7] virtio: use io_tlb_high

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Date:   Wed, 8 Jun 2022 22:07:06 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Dongli Zhang <dongli.zhang@...cle.com>
Cc:     iommu@...ts.linux-foundation.org, xen-devel@...ts.xenproject.org,
        x86@...nel.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, hch@...radead.org,
        m.szyprowski@...sung.com, jgross@...e.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        sstabellini@...nel.org, mpe@...erman.id.au, konrad.wilk@...cle.com,
        mst@...hat.com, jasowang@...hat.com, joe.jin@...cle.com
Subject: Re: [PATCH RFC v1 6/7] virtio: use io_tlb_high_mem if it is active

On Wed, Jun 08, 2022 at 05:55:52PM -0700, Dongli Zhang wrote:
>  /* Unique numbering for virtio devices. */
> @@ -241,6 +243,12 @@ static int virtio_dev_probe(struct device *_d)
>  	u64 device_features;
>  	u64 driver_features;
>  	u64 driver_features_legacy;
> +	struct device *parent = dev->dev.parent;
> +	u64 dma_mask = min_not_zero(*parent->dma_mask,
> +				    parent->bus_dma_limit);
> +
> +	if (dma_mask == DMA_BIT_MASK(64))
> +		swiotlb_use_high(parent);

The driver already very clearly communicated its addressing
requirements.  The underlying swiotlb code needs to transparently
pick the right pool.