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From: Tom Lendacky <thomas.lendacky@amd.com>
To: Baoquan He <bhe@redhat.com>, rientjes@google.com
Cc: Robin Murphy <robin.murphy@arm.com>,
	Christoph Hellwig <hch@infradead.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org,
	rppt@linux.ibm.com, brijesh.singh@amd.com,
	kexec@lists.infradead.org, iommu@lists.linux-foundation.org,
	m.szyprowski@samsung.com
Subject: Re: [PATCH RFC 0/2] dma-pool: allow user to disable atomic pool
Date: Wed, 11 Aug 2021 08:46:27 -0500	[thread overview]
Message-ID: <615cfd68-b1c2-f2d0-0c03-1271a913cef2@amd.com> (raw)
In-Reply-To: <20210811022327.GF23322@MiWiFi-R3L-srv>

On 8/10/21 9:23 PM, Baoquan He wrote:
> On 08/10/21 at 03:52pm, Tom Lendacky wrote:
>> On 8/5/21 1:54 AM, Baoquan He wrote:
>>> On 06/24/21 at 11:47am, Robin Murphy wrote:
>>>> On 2021-06-24 10:29, Baoquan He wrote:
>>>>> On 06/24/21 at 08:40am, Christoph Hellwig wrote:

...

> Looking at the those related commits, the below one from David tells 
> that atomic dma pool is used when device require non-blocking and
> unencrypted buffer. When I checked the system I borrowed, it's AMD EYPC
> and SME is enabled. And it has many pci devices, as you can see, its 'ls
> pci' outputs 113 lines. But disabling the three atomic pools didn't
> trigger any error on that AMD system. Does it mean only specific devices
> need this atomic pool in SME/SEV enabling case? Should we add more
> details in document or code comment to make clear this? 

It very well could be just the devices being used. Under SME (bare metal),
if a device supports 64-bit DMA, then bounce buffers aren't used and the
DMA can be performed directly to encrypted memory, so there is no need to
issue a set_memory_decrypted() call, so I would assume it likely isn't
using the pool.

Under SEV, however, all DMA has to go through guest un-encrypted memory.
If you pass through a device that does dma_alloc_coherent() calls with
GFP_ATOMIC, then the pool will be needed.

Thanks,
Tom

  reply	other threads:[~2021-08-11 13:46 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-24  5:20 Baoquan He
2021-06-24  5:20 ` [PATCH 1/2] docs: kernel-parameters: Update to reflect the current default size of " Baoquan He
2021-06-24  5:20 ` [PATCH 2/2] dma-pool: allow user to disable " Baoquan He
2021-06-24  7:40 ` [PATCH RFC 0/2] " Christoph Hellwig
2021-06-24  9:29   ` Baoquan He
2021-06-24 10:47     ` Robin Murphy
2021-06-24 12:10       ` Christoph Hellwig
2021-08-05  6:54       ` Baoquan He
2021-08-10 20:52         ` Tom Lendacky
2021-08-11  2:23           ` Baoquan He
2021-08-11 13:46             ` Tom Lendacky [this message]
2021-08-11  5:52           ` Christoph Hellwig

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