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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>, Paul Durrant <paul@xen.org>,
	xen-devel@lists.xenproject.org
Subject: Re: [for-4.15][RESEND PATCH v4 1/2] xen/x86: iommu: Ignore IOMMU mapping requests when a domain is dying
Date: Thu, 25 Feb 2021 14:18:44 +0100	[thread overview]
Message-ID: <2c1d2b05-7553-5f15-ad28-47aba5b9c47f@suse.com> (raw)
In-Reply-To: <7ce1deb9-e362-439c-dd14-a17dbb6fb1c8@xen.org>

On 25.02.2021 12:56, Julien Grall wrote:
> On 24/02/2021 14:07, Jan Beulich wrote:
>> On 24.02.2021 10:43, Julien Grall wrote:
>>> --- a/xen/drivers/passthrough/x86/iommu.c
>>> +++ b/xen/drivers/passthrough/x86/iommu.c
>>> @@ -267,6 +267,12 @@ int iommu_free_pgtables(struct domain *d)
>>>       struct page_info *pg;
>>>       unsigned int done = 0;
>>>   
>>> +    if ( !is_iommu_enabled(d) )
>>> +        return 0;
>>
>> Why is this addition needed? Hitting a not yet initialize spin lock
>> is - afaict - no worse than a not yet initialized list, so it would
>> seem to me that this can't be the reason. No other reason looks to
>> be called out by the description.
> 
> struct domain_iommu will be initially zeroed as it is part of struct domain.
> 
> For the list, we are so far fine because page_list_remove_head() 
> tolerates NULL. If we were using the normal list operations (e.g. 
> list_del), then this code would have segfaulted.

And so we do, in the CONFIG_BIGMEM case. May I suggest then to split
this out as a prereq patch, or add wording to the description
mentioning this additional effect?

Jan


  reply	other threads:[~2021-02-25 13:18 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-24  9:43 [for-4.15][RESEND PATCH v4 0/2] xen/iommu: Collection of bug fixes for IOMMU teardown Julien Grall
2021-02-24  9:43 ` [for-4.15][RESEND PATCH v4 1/2] xen/x86: iommu: Ignore IOMMU mapping requests when a domain is dying Julien Grall
2021-02-24 14:07   ` Jan Beulich
2021-02-25 11:56     ` Julien Grall
2021-02-25 13:18       ` Jan Beulich [this message]
2021-02-26 10:47         ` Julien Grall
2021-02-24  9:43 ` [for-4.15][RESEND PATCH v4 2/2] xen/iommu: x86: Clear the root page-table before freeing the page-tables Julien Grall
     [not found]   ` <c666bf75-451d-fbc1-7fb1-600c4f014f05@suse.com>
2021-02-24 16:00     ` Jan Beulich
2021-02-25 12:01       ` Julien Grall
2021-02-25 13:20         ` Jan Beulich
2021-02-24 11:01 ` [for-4.15][RESEND PATCH v4 0/2] xen/iommu: Collection of bug fixes for IOMMU teardown Ian Jackson

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