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From: Christoph Hellwig <hch@lst.de>
To: David Rientjes <rientjes@google.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Cc: Amit Pundir <amit.pundir@linaro.org>,
	jeremy.linton@arm.com, iommu@lists.linux-foundation.org,
	linux-rpi-kernel@lists.infradead.org,
	Robin Murphy <robin.murphy@arm.com>,
	Christoph Hellwig <hch@lst.de>
Subject: revert scope for 5.8, was Re: dma-pool fixes
Date: Sat, 1 Aug 2020 10:57:06 +0200	[thread overview]
Message-ID: <20200801085706.GA2991@lst.de> (raw)
In-Reply-To: <alpine.DEB.2.23.453.2008010105560.4078406@chino.kir.corp.google.com>

On Sat, Aug 01, 2020 at 01:20:07AM -0700, David Rientjes wrote:
> To follow-up on this, the introduction of the DMA atomic pools in 5.8 
> fixes an issue for any AMD SEV enabled guest that has a driver that 
> requires atomic DMA allocations (for us, nvme) because runtime decryption 
> of memory allocated through the DMA API may block.  This manifests itself 
> as "sleeping in invalid context" BUGs for any confidential VM user in 
> cloud.
> 
> I unfortunately don't have Amit's device to be able to independently debug 
> this issue and certainly could not have done a better job at working the 
> bug than Nicolas and Christoph have done so far.  I'm as baffled by the 
> results as anybody else.
> 
> I fully understand the no regressions policy.  I'd also ask that we 
> consider that *all* SEV guests are currently broken if they use nvme or 
> any other driver that does atomic DMA allocations.  It's an extremely 
> serious issue for cloud.  If there is *anything* that I can do to make 
> forward progress on this issue for 5.8, including some of the workarounds 
> above that Amit requested, I'd be very happy to help.  Christoph will make 
> the right decision for DMA in 5.8, but I simply wanted to state how 
> critical working SEV guests are to users.

I'm between a rock and a hard place here.  If we simply want to revert
commits as-is to make sure both the Raspberry Pi 4 and thone phone do
not regress we'll have to go all the way back and revert the whole SEV
pool support.  I could try to manual revert of the multiple pool
support, but it is very late for that.

Or maybe Linus has decided to cut a -rc8 which would give us a little
more time.
-
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  reply	other threads:[~2020-08-01  8:57 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-28 10:47 dma-pool fixes Christoph Hellwig
2020-07-28 10:47 ` [PATCH 1/2] dma-pool: fix coherent pool allocations for IOMMU mappings Christoph Hellwig
2020-07-28 14:56   ` Nicolas Saenz Julienne
2020-07-28 15:28     ` Christoph Hellwig
2020-07-28 10:47 ` [PATCH 2/2] dma-pool: Only allocate from CMA when in same memory zone Christoph Hellwig
2020-07-28 12:02 ` dma-pool fixes Amit Pundir
2020-07-28 12:07   ` Christoph Hellwig
2020-07-28 12:25     ` Amit Pundir
2020-07-28 12:41       ` Christoph Hellwig
2020-07-28 12:48         ` Amit Pundir
2020-07-28 15:30           ` Christoph Hellwig
2020-07-29 10:45             ` Nicolas Saenz Julienne
2020-07-29 12:22               ` Amit Pundir
2020-07-31  7:46                 ` Amit Pundir
2020-07-31 13:09                   ` Christoph Hellwig
2020-07-31 14:15                     ` Amit Pundir
2020-07-31 19:04                     ` David Rientjes via iommu
2020-08-01  8:20                       ` David Rientjes via iommu
2020-08-01  8:57                         ` Christoph Hellwig [this message]
2020-08-01 11:57                           ` revert scope for 5.8, was " Amit Pundir
2020-08-01 16:59                             ` Nicolas Saenz Julienne
2020-08-01 17:39                             ` Christoph Hellwig
2020-08-02  4:46                               ` Amit Pundir
2020-08-02 15:04                                 ` Amit Pundir
2020-08-03  4:14                                   ` David Rientjes via iommu
2020-08-03  6:44                                     ` Christoph Hellwig
2020-08-03 18:30                                       ` David Rientjes via iommu
2020-08-01 18:28                             ` Linus Torvalds
2020-08-02  4:35                               ` Amit Pundir
2020-08-01  8:29                       ` Christoph Hellwig
2020-07-31 10:47                 ` Nicolas Saenz Julienne
2020-07-31 11:17                   ` Amit Pundir
2020-07-31 14:15                     ` Nicolas Saenz Julienne
2020-07-31 14:20                       ` Amit Pundir
2020-08-01  7:34                         ` Amit Pundir

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