linux-kernel - Re: [PATCH 10/22] swiotlb: refactor coherent buffer allocation

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Message-ID: <20180110154649.GA18529@lst.de>
Date:   Wed, 10 Jan 2018 16:46:49 +0100
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org,
        linux-arch@...r.kernel.org, linux-mips@...ux-mips.org,
        Michal Simek <monstr@...str.eu>, linux-ia64@...r.kernel.org,
        Christian König 
        <ckoenig.leichtzumerken@...il.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Konrad Rzeszutek Wilk <konrad@...nok.org>,
        Guan Xuetao <gxt@...c.pku.edu.cn>,
        linuxppc-dev@...ts.ozlabs.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 10/22] swiotlb: refactor coherent buffer allocation

On Wed, Jan 10, 2018 at 12:22:18PM +0000, Robin Murphy wrote:
>> +	if (phys_addr == SWIOTLB_MAP_ERROR)
>> +		goto out_warn;
>>   -		/* Confirm address can be DMA'd by device */
>> -		if (dev_addr + size - 1 > dma_mask) {
>> -			printk("hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx\n",
>> -			       (unsigned long long)dma_mask,
>> -			       (unsigned long long)dev_addr);
>> +	*dma_handle = swiotlb_phys_to_dma(dev, phys_addr);
>
> nit: this should probably go after the dma_coherent_ok() check (as with the 
> original logic).

But the originall logic also needs the dma_addr_t for the
dma_coherent_ok check:

		dev_addr = swiotlb_phys_to_dma(hwdev, paddr);
		/* Confirm address can be DMA'd by device */
		if (dev_addr + size - 1 > dma_mask) {
			...
			goto err_warn;
		}

or do you mean assining to *dma_handle?  The dma_handle is not
valid for a failure return, so I don't think this should matter.

>> +	if (ret) {
>> +		*dma_handle = swiotlb_virt_to_bus(hwdev, ret);
>> +		if (dma_coherent_ok(hwdev, *dma_handle, size)) {
>> +			memset(ret, 0, size);
>> +			return ret;
>> +		}
>
> Aren't we leaking the pages here?

Yes, that free_pages got lost somewhere in the rebases, I've added
it back.