linux-kernel - Re: [RFC 00/20] Introduce /dev/iommu for userspace I/O address space management

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Date:   Tue, 21 Sep 2021 10:45:08 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Liu Yi L <yi.l.liu@...el.com>
Cc:     alex.williamson@...hat.com, hch@....de, jasowang@...hat.com,
        joro@...tes.org, jean-philippe@...aro.org, kevin.tian@...el.com,
        parav@...lanox.com, lkml@...ux.net, pbonzini@...hat.com,
        lushenming@...wei.com, eric.auger@...hat.com, corbet@....net,
        ashok.raj@...el.com, yi.l.liu@...ux.intel.com,
        jun.j.tian@...el.com, hao.wu@...el.com, dave.jiang@...el.com,
        jacob.jun.pan@...ux.intel.com, kwankhede@...dia.com,
        robin.murphy@....com, kvm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, dwmw2@...radead.org,
        linux-kernel@...r.kernel.org, baolu.lu@...ux.intel.com,
        david@...son.dropbear.id.au, nicolinc@...dia.com
Subject: Re: [RFC 00/20] Introduce /dev/iommu for userspace I/O address space
 management

On Sun, Sep 19, 2021 at 02:38:28PM +0800, Liu Yi L wrote:
> Linux now includes multiple device-passthrough frameworks (e.g. VFIO and
> vDPA) to manage secure device access from the userspace. One critical task
> of those frameworks is to put the assigned device in a secure, IOMMU-
> protected context so user-initiated DMAs are prevented from doing harm to
> the rest of the system.

Some bot will probably send this too, but it has compile warnings and
needs to be rebased to 5.15-rc1

drivers/iommu/iommufd/iommufd.c:269:6: warning: variable 'ret' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
        if (refcount_read(&ioas->refs) > 1) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/iommu/iommufd/iommufd.c:277:9: note: uninitialized use occurs here
        return ret;
               ^~~
drivers/iommu/iommufd/iommufd.c:269:2: note: remove the 'if' if its condition is always true
        if (refcount_read(&ioas->refs) > 1) {
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/iommu/iommufd/iommufd.c:253:17: note: initialize the variable 'ret' to silence this warning
        int ioasid, ret;
                       ^
                        = 0
drivers/iommu/iommufd/iommufd.c:727:7: warning: variable 'ret' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
                if (idev->dev == dev || idev->dev_cookie == dev_cookie) {
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/iommu/iommufd/iommufd.c:767:17: note: uninitialized use occurs here
        return ERR_PTR(ret);
                       ^~~
drivers/iommu/iommufd/iommufd.c:727:3: note: remove the 'if' if its condition is always false
                if (idev->dev == dev || idev->dev_cookie == dev_cookie) {
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/iommu/iommufd/iommufd.c:727:7: warning: variable 'ret' is used uninitialized whenever '||' condition is true [-Wsometimes-uninitialized]
                if (idev->dev == dev || idev->dev_cookie == dev_cookie) {
                    ^~~~~~~~~~~~~~~~
drivers/iommu/iommufd/iommufd.c:767:17: note: uninitialized use occurs here
        return ERR_PTR(ret);
                       ^~~
drivers/iommu/iommufd/iommufd.c:727:7: note: remove the '||' if its condition is always false
                if (idev->dev == dev || idev->dev_cookie == dev_cookie) {
                    ^~~~~~~~~~~~~~~~~~~
drivers/iommu/iommufd/iommufd.c:717:9: note: initialize the variable 'ret' to silence this warning
        int ret;
               ^
                = 0

Jason