RE: [PATCH 09/17] mm: export access_remote_vm() symbol

From: "Yu, Fenghua" <fenghua.yu@intel.com>
To: Alistair Popple <apopple@nvidia.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>,
	Vinod Koul <vkoul@kernel.org>,
	"Jiang, Dave" <dave.jiang@intel.com>,
	"dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>,
	"Zhu, Tony" <tony.zhu@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Christoph Hellwig <hch@infradead.org>,
	"Shankar, Ravi V" <ravi.v.shankar@intel.com>
Subject: RE: [PATCH 09/17] mm: export access_remote_vm() symbol
Date: Thu, 5 Jan 2023 20:58:08 +0000	[thread overview]
Message-ID: <IA1PR11MB6097D5C6C3182A3C782E99D89BFA9@IA1PR11MB6097.namprd11.prod.outlook.com> (raw)
In-Reply-To: <87tu15u061.fsf@nvidia.com>

Hi, Alistair,

> >> Alistair Popple <apopple@nvidia.com> writes:
> >> Lorenzo Stoakes <lstoakes@gmail.com> writes:
> >> > My concern is exposing something highly delicate _which accesses
> >> > remote mas a public API with implicit assumptions whose one and
> >> > only (core kernel) user treats with enormous caution. Even if this
> >> > iommu code were to use it correctly, we'd end up with an interface
> >> > which could be
> >> subject to real risks which other drivers may misuse.
> >>
> >> Ok, although I think making this an iommu specific wrapper taking a
> >> PASID rather than mm_struct would make the API more specific and less
> >> likely to be misused as the mm_count/users lifetime issues could be
> >> dealt with inside the core IOMMU code.
> >
> > The iommu specific wrapper still needs to call access_remote_vm()
> > which is in generic mm. We cannot avoid to export access_remote_vm(), right?
> 
> The wrapper still needs to call access_remote_vm(), but that doesn't imply
> access_remote_vm() needs to be exported. I think the logical place to put the
> wrapper would be in iommu-sva.c which isn't built as a module, so you would
> only have to EXPORT_SYMBOL_GPL the wrapper and not access_remote_vm().

This looks better than exporting access_remote_vm(). I will remove this patch
and write the IOMMU wrapper to call access_remote_vm() in v2.

Thanks.

-Fenghua