From: Tom Lendacky <thomas.lendacky@amd.com>
To: Baoquan He <bhe@redhat.com>, Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@infradead.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org,
rientjes@google.com, 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: Tue, 10 Aug 2021 15:52:25 -0500 [thread overview]
Message-ID: <5df93c4e-ffdd-88c5-db4a-1a09826d047a@amd.com> (raw)
In-Reply-To: <20210805065410.GA2051@MiWiFi-R3L-srv>
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:
>>>> So reduce the amount allocated. But the pool is needed for proper
>>>> operation on systems with memory encryption. And please add the right
>>>> maintainer or at least mailing list for the code you're touching next
>>>> time.
>>>
>>> Oh, I thoutht it's memory issue only, should have run
>>> ./scripts/get_maintainer.pl. sorry.
>>>
>>> About reducing the amount allocated, it may not help. Because on x86_64,
>>> kdump kernel doesn't put any page of memory into buddy allocator of DMA
>>> zone. Means it will defenitely OOM for atomic_pool_dma initialization.
>>>
>>> Wondering in which case or on which device the atomic pool is needed on
>>> AMD system with mem encrytion enabled. As we can see, the OOM will
>>> happen too in kdump kernel on Intel system, even though it's not
>>> necessary.
>
> Sorry for very late response, and thank both for your comments.
>
>>
>> Hmm, I think the Kconfig reshuffle has actually left a slight wrinkle here.
>> For DMA_DIRECT_REMAP=y we can assume an atomic pool is always needed, since
>> that was the original behaviour anyway. However the implications of
>> AMD_MEM_ENCRYPT=y are different - even if support is enabled, it still
>> should only be relevant if mem_encrypt_active(), so it probably does make
>> sense to have an additional runtime gate on that.
>
>>
>> From a quick scan, use of dma_alloc_from_pool() already depends on
>> force_dma_unencrypted() so that's probably fine already, but I think we'd
>> need a bit of extra protection around dma_free_from_pool() to prevent
>> gen_pool_has_addr() dereferencing NULL if the pools are uninitialised, even
>> with your proposed patch as it is. Presumably nothing actually called
>> dma_direct_free() when you tested this?
>
> Yes, enforcing the conditional check of force_dma_unencrypted() around
> dma_free_from_pool sounds reasonable, just as we have done in
> dma_alloc_from_pool().
>
> I have tested this patchset on normal x86_64 systems and one amd system
> with SME support, disabling atomic pool can fix the issue that there's no
> managed pages in dma zone then requesting page from dma zone will cause
> allocation failure. And even disabling atomic pool in 1st kernel didn't
> cause any problem on one AMD EPYC system which supports SME. I am not
> expert of DMA area, wondering how atomic pool is supposed to do in
> SME/SEV system.
I think the atomic pool is used by the NVMe driver. My understanding is
that driver will do a dma_alloc_coherent() from interrupt context, so it
needs to use GFP_ATOMIC. The pool was created because dma_alloc_coherent()
would perform a set_memory_decrypted() call, which can sleep. The pool
eliminates that issue (David can correct me if I got that wrong).
Thanks,
Tom
>
> Besides, even though atomic pool is disabled, slub page for allocation
> of dma-kmalloc also triggers page allocation failure. So I change to
> take another way to fix them, please check v2 post. The atomic pool
> disabling an be a good to have change.
>
> Thanks
> Baoquan
>
next prev parent reply other threads:[~2021-08-10 20:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-24 5:20 [PATCH RFC 0/2] dma-pool: allow user to disable atomic pool 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 [this message]
2021-08-11 2:23 ` Baoquan He
2021-08-11 13:46 ` Tom Lendacky
2021-08-11 5:52 ` Christoph Hellwig
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5df93c4e-ffdd-88c5-db4a-1a09826d047a@amd.com \
--to=thomas.lendacky@amd.com \
--cc=bhe@redhat.com \
--cc=brijesh.singh@amd.com \
--cc=hch@infradead.org \
--cc=iommu@lists.linux-foundation.org \
--cc=kexec@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=m.szyprowski@samsung.com \
--cc=rientjes@google.com \
--cc=robin.murphy@arm.com \
--cc=rppt@linux.ibm.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).