Re: [PATCH v5 07/19] kernel/user: Allow user::locked_vm to be usable for iommufd

From: Eric Auger <eric.auger@redhat.com>
To: Jason Gunthorpe <jgg@nvidia.com>,
	bpf@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
	David Woodhouse <dwmw2@infradead.org>,
	iommu@lists.linux.dev, Joerg Roedel <joro@8bytes.org>,
	Kevin Tian <kevin.tian@intel.com>,
	linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
	llvm@lists.linux.dev, Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Miguel Ojeda <ojeda@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Shuah Khan <shuah@kernel.org>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	Tom Rix <trix@redhat.com>, Will Deacon <will@kernel.org>
Cc: Anthony Krowiak <akrowiak@linux.ibm.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	Bagas Sanjaya <bagasdotme@gmail.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Chaitanya Kulkarni <chaitanyak@nvidia.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	David Gibson <david@gibson.dropbear.id.au>,
	Eric Farman <farman@linux.ibm.com>,
	Jason Wang <jasowang@redhat.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Jason Herne <jjherne@linux.ibm.com>,
	Joao Martins <joao.m.martins@oracle.com>,
	kvm@vger.kernel.org, Lixiao Yang <lixiao.yang@intel.com>,
	Matthew Rosato <mjrosato@linux.ibm.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Nicolin Chen <nicolinc@nvidia.com>,
	Halil Pasic <pasic@linux.ibm.com>,
	Niklas Schnelle <schnelle@linux.ibm.com>,
	Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
	Yi Liu <yi.l.liu@intel.com>, Keqian Zhu <zhukeqian1@huawei.com>
Subject: Re: [PATCH v5 07/19] kernel/user: Allow user::locked_vm to be usable for iommufd
Date: Fri, 18 Nov 2022 10:09:26 +0100	[thread overview]
Message-ID: <569b4eeb-792a-9ad6-d52e-555f987bc7f7@redhat.com> (raw)
In-Reply-To: <7-v5-4001c2997bd0+30c-iommufd_jgg@nvidia.com>

Hi Jason,

On 11/16/22 22:00, Jason Gunthorpe wrote:
> Following the pattern of io_uring, perf, skb, and bpf iommfd will use
> user->locked_vm for accounting pinned pages. Ensure the value is included
> in the struct and export free_uid() as iommufd is modular.
>
> user->locked_vm is the good accounting to use for ulimit because it is
> per-user, and the security sandboxing of locked pages is not supposed to
> be per-process. Other places (vfio, vdpa and infiniband) have used
> mm->pinned_vm and/or mm->locked_vm for accounting pinned pages, but this
> is only per-process and inconsistent with the new FOLL_LONGTERM users in
> the kernel.
>
> Concurrent work is underway to try to put this in a cgroup, so everything
> can be consistent and the kernel can provide a FOLL_LONGTERM limit that
> actually provides security.
>
> Tested-by: Nicolin Chen <nicolinc@nvidia.com>
> Tested-by: Yi Liu <yi.l.liu@intel.com>
> Tested-by: Lixiao Yang <lixiao.yang@intel.com>
> Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Reviewed-by: Eric Auger <eric.auger@redhat.com>

Eric
> ---
>  include/linux/sched/user.h | 2 +-
>  kernel/user.c              | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
> index f054d0360a7533..4cc52698e214e2 100644
> --- a/include/linux/sched/user.h
> +++ b/include/linux/sched/user.h
> @@ -25,7 +25,7 @@ struct user_struct {
>  
>  #if defined(CONFIG_PERF_EVENTS) || defined(CONFIG_BPF_SYSCALL) || \
>  	defined(CONFIG_NET) || defined(CONFIG_IO_URING) || \
> -	defined(CONFIG_VFIO_PCI_ZDEV_KVM)
> +	defined(CONFIG_VFIO_PCI_ZDEV_KVM) || IS_ENABLED(CONFIG_IOMMUFD)
>  	atomic_long_t locked_vm;
>  #endif
>  #ifdef CONFIG_WATCH_QUEUE
> diff --git a/kernel/user.c b/kernel/user.c
> index e2cf8c22b539a7..d667debeafd609 100644
> --- a/kernel/user.c
> +++ b/kernel/user.c
> @@ -185,6 +185,7 @@ void free_uid(struct user_struct *up)
>  	if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
>  		free_user(up, flags);
>  }
> +EXPORT_SYMBOL_GPL(free_uid);
>  
>  struct user_struct *alloc_uid(kuid_t uid)
>  {