Re: [PATCH 10/10] vfio/qat: Add vfio_pci driver for Intel QAT VF devices

From: Jason Gunthorpe <jgg@nvidia.com>
To: "Zeng, Xin" <xin.zeng@intel.com>
Cc: Yishai Hadas <yishaih@nvidia.com>,
	"herbert@gondor.apana.org.au" <herbert@gondor.apana.org.au>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"shameerali.kolothum.thodi@huawei.com"
	<shameerali.kolothum.thodi@huawei.com>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	qat-linux <qat-linux@intel.com>,
	"Cao, Yahui" <yahui.cao@intel.com>
Subject: Re: [PATCH 10/10] vfio/qat: Add vfio_pci driver for Intel QAT VF devices
Date: Tue, 20 Feb 2024 09:24:59 -0400	[thread overview]
Message-ID: <20240220132459.GM13330@nvidia.com> (raw)
In-Reply-To: <DM4PR11MB550274B713F6AE416CDF7FDB88532@DM4PR11MB5502.namprd11.prod.outlook.com>

On Sat, Feb 17, 2024 at 04:20:20PM +0000, Zeng, Xin wrote:

> Thanks for this information, but this flow is not clear to me why it 
> cause deadlock. From this flow, CPU0 is not waiting for any resource
> held by CPU1, so after CPU0 releases mmap_lock, CPU1 can continue
> to run. Am I missing something?

At some point it was calling copy_to_user() under the state
mutex. These days it doesn't.

copy_to_user() would nest the mm_lock under the state mutex which is a
locking inversion.

So I wonder if we still have this problem now that the copy_to_user()
is not under the mutex?

Jason