From: Jan Beulich <jbeulich@suse.com>
To: Julien Grall <julien@xen.org>
Cc: hongyxia@amazon.co.uk, iwj@xenproject.org,
Julien Grall <jgrall@amazon.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Kevin Tian <kevin.tian@intel.com>,
xen-devel@lists.xenproject.org, Paul Durrant <paul@xen.org>
Subject: Re: [for-4.15][PATCH v3 2/3] xen/x86: iommu: Ignore IOMMU mapping requests when a domain is dying
Date: Fri, 19 Feb 2021 09:49:54 +0100 [thread overview]
Message-ID: <aa672eaa-e828-968b-73bf-dd4249d5de16@suse.com> (raw)
In-Reply-To: <c713f440-8c3d-42fe-1d71-56b23e53a495@xen.org>
On 18.02.2021 14:25, Julien Grall wrote:
> Hi,
>
> On 18/02/2021 13:05, Jan Beulich wrote:
>> On 17.02.2021 17:07, Julien Grall wrote:
>>> On 17/02/2021 15:01, Jan Beulich wrote:
>>>> On 17.02.2021 15:24, Julien Grall wrote:
>>>>> From: Julien Grall <jgrall@amazon.com>
>>>>>
>>>>> The new x86 IOMMU page-tables allocator will release the pages when
>>>>> relinquishing the domain resources. However, this is not sufficient
>>>>> when the domain is dying because nothing prevents page-table to be
>>>>> allocated.
>>>>>
>>>>> Currently page-table allocations can only happen from iommu_map(). As
>>>>> the domain is dying, there is no good reason to continue to modify the
>>>>> IOMMU page-tables.
>>>>
>>>> While I agree this to be the case right now, I'm not sure it is a
>>>> good idea to build on it (in that you leave the unmap paths
>>>> untouched).
>>>
>>> I don't build on that assumption. See next patch.
>>
>> Yet as said there that patch makes unmapping perhaps more fragile,
>> by introducing a latent error source into the path.
>
> I still don't see what latent error my patch will introduce. Allocation
> of page-tables are not guarantee to succeed.
>
> So are you implying that a code may rely on the page allocation to succeed?
I'm implying that failure to split a superpage may have unknown
consequences. Since we make no use of superpages when not
sharing page tables, I call this a latent issue which may go
unnoticed for quite some time once no longer latent.
Jan
next prev parent reply other threads:[~2021-02-19 8:50 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-17 14:24 [for-4.15][PATCH v3 0/3] xen/iommu: Collection of bug fixes for IOMMU teadorwn Julien Grall
2021-02-17 14:24 ` [for-4.15][PATCH v3 1/3] xen/iommu: x86: Clear the root page-table before freeing the page-tables Julien Grall
2021-02-17 14:54 ` Jan Beulich
2021-02-17 15:00 ` Julien Grall
2021-02-17 15:17 ` Jan Beulich
2021-02-17 16:48 ` Julien Grall
2021-02-17 14:24 ` [for-4.15][PATCH v3 2/3] xen/x86: iommu: Ignore IOMMU mapping requests when a domain is dying Julien Grall
2021-02-17 15:01 ` Jan Beulich
2021-02-17 16:07 ` Julien Grall
2021-02-18 13:05 ` Jan Beulich
2021-02-18 13:25 ` Julien Grall
2021-02-19 8:49 ` Jan Beulich [this message]
2021-02-19 9:24 ` Julien Grall
2021-02-18 14:00 ` Paul Durrant
2021-02-19 8:56 ` Jan Beulich
2021-02-17 14:24 ` [for-4.15][PATCH v3 3/3] xen/iommu: x86: Harden the IOMMU page-table allocator Julien Grall
2021-02-17 15:13 ` Jan Beulich
2021-02-17 16:29 ` Julien Grall
2021-02-18 13:10 ` Jan Beulich
2021-02-18 13:19 ` Julien Grall
2021-02-18 17:04 ` Jan Beulich
2021-02-18 17:41 ` Julien Grall
2021-02-19 8:46 ` Jan Beulich
2021-02-19 8:57 ` Julien Grall
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