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From: Jason Gunthorpe <jgg@nvidia.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Tom Lendacky <thomas.lendacky@amd.com>, <x86@kernel.org>,
	<linux-kernel@vger.kernel.org>, <linux-arch@vger.kernel.org>,
	<linux-mm@kvack.org>, <kvm@vger.kernel.org>,
	Radim Kr??m???? <rkrcmar@redhat.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Andy Lutomirski <luto@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	"Alexander Potapenko" <glider@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Dmitry Vyukov" <dvyukov@google.com>,
	Rik van Riel <riel@redhat.com>,
	Larry Woodman <lwoodman@redhat.com>,
	Dave Young <dyoung@redhat.com>,
	Toshimitsu Kani <toshi.kani@hpe.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Brijesh Singh <brijesh.singh@amd.com>
Subject: Re: AMD SME encrpytion and PCI BAR pages to user space
Date: Tue, 27 Oct 2020 08:58:10 -0300	[thread overview]
Message-ID: <20201027115810.GH1523783@nvidia.com> (raw)
In-Reply-To: <20201027084357.GA10053@infradead.org>

On Tue, Oct 27, 2020 at 08:43:57AM +0000, Christoph Hellwig wrote:
> On Wed, Oct 21, 2020 at 01:03:22PM -0300, Jason Gunthorpe wrote:
> > Oh, interesting.. Yes the issue is no userspace DMA stuff uses the DMA
> > API correctly (because it is in userspace)
> > 
> > So SWIOTLB tricks don't work, I wish the dma_map could fail for these
> > situations
> 
> Userspace DMA by definition also does not use dma_map..

? Sure it does, ib_dma_map_sg_attrs() is what RDMA uses

What all the userspace users skip is the dma_sync*() - that would
require a kernel call which defeats the point.

So, my desire is some flag to dma_map_sg() that says
  'user space mapping no dma_sync_*'

ie dma_sync_* is a NOP

Then things like SWIOTLB on the SEV system can fail with an error code
instead of malfunctioning

If FOLL_LONGERM is some estimate of this pattern then we have these users:
 - drivers/infiniband
 - v4l
 - vdpa
 - xdp
 - rds
 - habana labs

Jason

      reply	other threads:[~2020-10-27 11:58 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-19 15:25 AMD SME encrpytion and PCI BAR pages to user space Jason Gunthorpe
2020-10-19 16:36 ` Tom Lendacky
2020-10-19 17:00   ` Jason Gunthorpe
2020-10-19 17:11     ` Tom Lendacky
2020-10-19 17:25       ` Jason Gunthorpe
2020-10-21 11:59   ` Jason Gunthorpe
2020-10-21 15:30     ` Tom Lendacky
2020-10-21 16:03       ` Jason Gunthorpe
2020-10-27  8:43         ` Christoph Hellwig
2020-10-27 11:58           ` Jason Gunthorpe [this message]

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