linux-kernel - Re: [PATCH 1/2] dma-mapping: support setting memory uncached in place

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200221141656.GF6968@lst.de>
Date:   Fri, 21 Feb 2020 15:16:56 +0100
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@....de>, Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        openrisc@...ts.librecores.org, iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dma-mapping: support setting memory uncached in
 place

On Thu, Feb 20, 2020 at 05:21:35PM +0000, Robin Murphy wrote:
>> @@ -196,10 +192,15 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
>>     	memset(ret, 0, size);
>>   -	if (IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT) &&
>> -	    dma_alloc_need_uncached(dev, attrs)) {
>> +	if (dma_alloc_need_uncached(dev, attrs)) {
>>   		arch_dma_prep_coherent(page, size);
>> -		ret = uncached_kernel_address(ret);
>> +
>> +		if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED)) {
>> +			if (!arch_dma_set_uncached(ret, size))
>> +				goto out_free_pages;
>> +		} else if (IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT)) {
>> +			ret = uncached_kernel_address(ret);
>
> Hmm, would we actually need to keep ARCH_HAS_UNCACHED_SEGMENT? If 
> arch_dma_set_uncached() returned void*/ERR_PTR instead, then it could work 
> for both cases (with arch_dma_clear_uncached() being a no-op for segments).

Yes, I think so.  I was a little worried about what to do with
cached_kernel_address() in that scheme, but it turns out with the recent
round of dma-direct cleanup that is actually entirely unused now.