linux-kernel - Re: [PATCH v13 3/8] iommu/vt-d: Add nested translation helper function

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Date:   Thu, 14 May 2020 08:31:43 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Eric Auger <eric.auger@...hat.com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jonathan Cameron <jic23@...nel.org>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v13 3/8] iommu/vt-d: Add nested translation helper
 function

On Wed, 13 May 2020 22:54:24 -0700
Christoph Hellwig <hch@...radead.org> wrote:

> > +	 * 1. CPU vs. IOMMU
> > +	 * 2. Guest vs. Host.
> > +	 */
> > +	switch (addr_width) {
> > +#ifdef CONFIG_X86
> > +	case ADDR_WIDTH_5LEVEL:
> > +		if (cpu_feature_enabled(X86_FEATURE_LA57) &&
> > +		    cap_5lp_support(iommu->cap)) {
> > +			pasid_set_flpm(pte, 1);
> > +		} else {
> > +			dev_err_ratelimited(dev, "5-level paging
> > not supported\n");
> > +			return -EINVAL;
> > +		}
> > +		break;  
> 
> The normal style would be to handle the early error return first:
> 
> 		if (!cpu_feature_enabled(X86_FEATURE_LA57) ||
> 		    !cap_5lp_support(iommu->cap)) {
> 			dev_err_ratelimited(dev,
> 				"5-level paging not supported\n");
> 			return -EINVAL;
> 		}
> 
> 		pasid_set_flpm(pte, 1);
> 		break;
> 

Sounds good. I was thinking in positive logic.

thanks