Re: [PATCH 1/8] iommu/vt-d: clean up 32bit si_domain assignment

From: Arvind Sankar <nivedita@alum.mit.edu>
To: Tom Murphy <murphyt7@tcd.ie>
Cc: Heiko Stuebner <heiko@sntech.de>,
	kvm@vger.kernel.org, David Airlie <airlied@linux.ie>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
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	Bjorn Andersson <bjorn.andersson@linaro.org>,
	linux-tegra@vger.kernel.org, Julien Grall <julien.grall@arm.com>,
	Thierry Reding <thierry.reding@gmail.com>,
	Will Deacon <will@kernel.org>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	linux-samsung-soc@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
	iommu@lists.linux-foundation.org,
	Krzysztof Kozlowski <krzk@kernel.org>,
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	Andy Gross <agross@kernel.org>,
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	Daniel Vetter <daniel@ffwll.ch>,
	Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH 1/8] iommu/vt-d: clean up 32bit si_domain assignment
Date: Sat, 21 Dec 2019 18:46:37 -0500	[thread overview]
Message-ID: <20191221234635.GA99623@rani.riverdale.lan> (raw)
In-Reply-To: <20191221150402.13868-2-murphyt7@tcd.ie>

On Sat, Dec 21, 2019 at 03:03:53PM +0000, Tom Murphy wrote:
> In the intel iommu driver devices which only support 32bit DMA can't be
> direct mapped. The implementation of this is weird. Currently we assign
> it a direct mapped domain and then remove the domain later and replace
> it with a domain of type IOMMU_DOMAIN_IDENTITY. We should just assign it
> a domain of type IOMMU_DOMAIN_IDENTITY from the begging rather than
> needlessly swapping domains.
> 
> Signed-off-by: Tom Murphy <murphyt7@tcd.ie>
> ---
>  drivers/iommu/intel-iommu.c | 88 +++++++++++++------------------------
>  1 file changed, 31 insertions(+), 57 deletions(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 0c8d81f56a30..c1ea66467918 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -5640,7 +5609,12 @@ static int intel_iommu_add_device(struct device *dev)
>  	domain = iommu_get_domain_for_dev(dev);
>  	dmar_domain = to_dmar_domain(domain);
>  	if (domain->type == IOMMU_DOMAIN_DMA) {
> -		if (device_def_domain_type(dev) == IOMMU_DOMAIN_IDENTITY) {
> +		/*
> +		 * We check dma_mask >= dma_get_required_mask(dev) because
> +		 * 32 bit DMA falls back to non-identity mapping.
> +		 */
> +		if (device_def_domain_type(dev) == IOMMU_DOMAIN_IDENTITY &&
> +				dma_mask >= dma_get_required_mask(dev)) {
>  			ret = iommu_request_dm_for_dev(dev);
>  			if (ret) {
>  				dmar_remove_one_dev_info(dev);
> -- 
> 2.20.1
> 

Should this be dma_direct_get_required_mask? dma_get_required_mask may
return DMA_BIT_MASK(32) -- it callbacks into intel_get_required_mask,
but I'm not sure what iommu_no_mapping(dev) will do at this point?
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