netdev - Re: [PATCH 1/8] iommu: Add a gfp parameter to iommu

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Message-ID: <Y8WTd/37G6lWA8c5@nvidia.com>
Date:   Mon, 16 Jan 2023 14:12:07 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        ath10k@...ts.infradead.org, ath11k@...ts.infradead.org,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        dri-devel@...ts.freedesktop.org, iommu@...ts.linux.dev,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-media@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-s390@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-tegra@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, nouveau@...ts.freedesktop.org,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 1/8] iommu: Add a gfp parameter to iommu_map()

On Fri, Jan 06, 2023 at 05:15:28PM +0000, Robin Murphy wrote:

> However, echoing the recent activity over on the DMA API side of things, I
> think it's still worth proactively constraining the set of permissible
> flags, lest we end up with more weird problems if stuff that doesn't really
> make sense, like GFP_COMP or zone flags, manages to leak through (that may
> have been part of the reason for having the current wrappers rather than a
> bare gfp argument in the first place, I forget now).

I did it like this:

--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -2368,6 +2368,11 @@ int iommu_map(struct iommu_domain *domain, unsigned long iova,
 
 	might_sleep_if(gfpflags_allow_blocking(gfp));
 
+	/* Discourage passing strange GFP flags */
+	if (WARN_ON_ONCE(gfp & (__GFP_COMP | __GFP_DMA | __GFP_DMA32 |
+				__GFP_HIGHMEM)))
+		return -EINVAL;
+
 	ret = __iommu_map(domain, iova, paddr, size, prot, gfp);
 	if (ret == 0 && ops->iotlb_sync_map)
 		ops->iotlb_sync_map(domain, iova, size);
@@ -2477,6 +2482,11 @@ ssize_t iommu_map_sg(struct iommu_domain *domain, unsigned long iova,
 
 	might_sleep_if(gfpflags_allow_blocking(gfp));
 
+	/* Discourage passing strange GFP flags */
+	if (WARN_ON_ONCE(gfp & (__GFP_COMP | __GFP_DMA | __GFP_DMA32 |
+				__GFP_HIGHMEM)))
+		return -EINVAL;
+
 	while (i <= nents) {
 		phys_addr_t s_phys = sg_phys(sg);
 
Will post a v2 when the driver people take a look

Thanks,
Jason