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

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Date:   Wed, 10 Jan 2018 17:02:30 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     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 10/01/18 15:46, Christoph Hellwig wrote:
> 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.

Yeah, only the assignment - as I said, it's just a stylistic nit; no big 
deal either way.

>>> +	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.

Cool.

Robin.