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From: Julien Grall <julien@xen.org>
To: Penny Zheng <Penny.Zheng@arm.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	"sstabellini@kernel.org" <sstabellini@kernel.org>
Cc: Bertrand Marquis <Bertrand.Marquis@arm.com>,
	Wei Chen <Wei.Chen@arm.com>, nd <nd@arm.com>
Subject: Re: [PATCH 05/10] xen/arm: introduce alloc_staticmem_pages
Date: Mon, 24 May 2021 11:24:42 +0100	[thread overview]
Message-ID: <d5da5783-be83-6162-e4ab-79326aac8edd@xen.org> (raw)
In-Reply-To: <VE1PR08MB521532DDD1CC4C8872AE08CFF7269@VE1PR08MB5215.eurprd08.prod.outlook.com>



On 24/05/2021 11:10, Penny Zheng wrote:
> Hi Julien

Hi Penny,

>>>> +    if ( !pg )
>>>> +        return NULL;
>>>> +
>>>> +    for ( i = 0; i < nr_pfns; i++)
>>>> +    {
>>>> +        /*
>>>> +         * Reference count must continuously be zero for free pages
>>>> +         * of static memory(PGC_reserved).
>>>> +         */
>>>> +        ASSERT(pg[i].count_info & PGC_reserved);
>>>> +        if ( (pg[i].count_info & ~PGC_reserved) != PGC_state_free )
>>>> +        {
>>>> +            printk(XENLOG_ERR
>>>> +                    "Reference count must continuously be zero for free pages"
>>>> +                    "pg[%u] MFN %"PRI_mfn" c=%#lx t=%#x\n",
>>>> +                    i, mfn_x(page_to_mfn(pg + i)),
>>>> +                    pg[i].count_info, pg[i].tlbflush_timestamp);
>>>> +            BUG();
>>>
>>> So we would crash Xen if the caller pass a wrong range. Is it what we want?
>>>
>>> Also, who is going to prevent concurrent access?
>>>
>>
>> Sure, to fix concurrency issue, I may need to add one spinlock like `static
>> DEFINE_SPINLOCK(staticmem_lock);`
>>
>> In current alloc_heap_pages, it will do similar check, that pages in free state
>> MUST have zero reference count. I guess, if condition not met, there is no need
>> to proceed.
>>
> 
> Another thought on concurrency problem, when constructing patch v2, do we need to
> consider concurrency here?
> heap_lock is to take care concurrent allocation on the one heap, but static memory is
> always reserved for only one specific domain.
In theory yes, but you are relying on the admin to correctly write the 
device-tree nodes.

You are probably not going to hit the problem today because the domains 
are created one by one. But, as you may want to allocate memory at 
runtime, this is quite important to get the code protected from 
concurrent access.

Here, you will likely want to use the heaplock rather than a new lock. 
So you are also protect against concurrent access to count_info from 
other part of Xen.


Cheers,

-- 
Julien Grall


  reply	other threads:[~2021-05-24 10:24 UTC|newest]

Thread overview: 82+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-18  5:21 [PATCH 00/10] Domain on Static Allocation Penny Zheng
2021-05-18  5:21 ` [PATCH 01/10] xen/arm: introduce domain " Penny Zheng
2021-05-18  8:58   ` Julien Grall
2021-05-19  2:22     ` Penny Zheng
2021-05-19 18:27       ` Julien Grall
2021-05-20  6:07         ` Penny Zheng
2021-05-20  8:50           ` Julien Grall
2021-06-02 10:09             ` Penny Zheng
2021-06-03  9:09               ` Julien Grall
2021-06-03 21:32                 ` Stefano Stabellini
2021-06-03 22:07                   ` Julien Grall
2021-06-03 23:55                     ` Stefano Stabellini
2021-06-04  4:00                       ` Penny Zheng
2021-06-05  2:00                         ` Stefano Stabellini
2021-06-07 18:09                       ` Julien Grall
2021-06-09  9:56                         ` Bertrand Marquis
2021-06-09 10:47                           ` Julien Grall
2021-06-15  6:08                             ` Penny Zheng
2021-06-17 11:22                               ` Julien Grall
2021-05-18  5:21 ` [PATCH 02/10] xen/arm: handle static memory in dt_unreserved_regions Penny Zheng
2021-05-18  9:04   ` Julien Grall
2021-05-18  5:21 ` [PATCH 03/10] xen/arm: introduce PGC_reserved Penny Zheng
2021-05-18  9:45   ` Julien Grall
2021-05-19  3:16     ` Penny Zheng
2021-05-19  9:49       ` Jan Beulich
2021-05-19 19:49         ` Julien Grall
2021-05-20  7:05           ` Jan Beulich
2021-05-19 19:46       ` Julien Grall
2021-05-20  6:19         ` Penny Zheng
2021-05-20  8:40           ` Penny Zheng
2021-05-20  8:59             ` Julien Grall
2021-05-20  9:27               ` Jan Beulich
2021-05-20  9:45                 ` Julien Grall
2021-05-18  5:21 ` [PATCH 04/10] xen/arm: static memory initialization Penny Zheng
2021-05-18  7:15   ` Jan Beulich
2021-05-18  9:51     ` Penny Zheng
2021-05-18 10:43       ` Jan Beulich
2021-05-20  9:04         ` Penny Zheng
2021-05-20  9:32           ` Jan Beulich
2021-05-18 10:00   ` Julien Grall
2021-05-18 10:01     ` Julien Grall
2021-05-19  5:02     ` Penny Zheng
2021-05-18  5:21 ` [PATCH 05/10] xen/arm: introduce alloc_staticmem_pages Penny Zheng
2021-05-18  7:24   ` Jan Beulich
2021-05-18  9:30     ` Penny Zheng
2021-05-18 10:09     ` Julien Grall
2021-05-18 10:15   ` Julien Grall
2021-05-19  5:23     ` Penny Zheng
2021-05-24 10:10       ` Penny Zheng
2021-05-24 10:24         ` Julien Grall [this message]
2021-05-18  5:21 ` [PATCH 06/10] xen: replace order with nr_pfns in assign_pages for better compatibility Penny Zheng
2021-05-18  7:27   ` Jan Beulich
2021-05-18  9:11     ` Penny Zheng
2021-05-18 10:20   ` Julien Grall
2021-05-19  5:35     ` Penny Zheng
2021-05-18  5:21 ` [PATCH 07/10] xen/arm: intruduce alloc_domstatic_pages Penny Zheng
2021-05-18  7:34   ` Jan Beulich
2021-05-18  8:57     ` Penny Zheng
2021-05-18 11:23       ` Jan Beulich
2021-05-21  6:41         ` Penny Zheng
2021-05-21  7:09           ` Jan Beulich
2021-06-03  2:44             ` Penny Zheng
2021-05-18 12:13       ` Julien Grall
2021-05-19  7:52         ` Penny Zheng
2021-05-19 20:01           ` Julien Grall
2021-05-18 10:30   ` Julien Grall
2021-05-19  6:03     ` Penny Zheng
2021-05-18  5:21 ` [PATCH 08/10] xen/arm: introduce reserved_page_list Penny Zheng
2021-05-18  7:39   ` Jan Beulich
2021-05-18  8:38     ` Penny Zheng
2021-05-18 11:24       ` Jan Beulich
2021-05-19  6:46         ` Penny Zheng
2021-05-18 11:02   ` Julien Grall
2021-05-19  6:43     ` Penny Zheng
2021-05-18  5:21 ` [PATCH 09/10] xen/arm: parse `xen,static-mem` info during domain construction Penny Zheng
2021-05-18 12:09   ` Julien Grall
2021-05-19  7:58     ` Penny Zheng
2021-05-18  5:21 ` [PATCH 10/10] xen/arm: introduce allocate_static_memory Penny Zheng
2021-05-18 12:05   ` Julien Grall
2021-05-19  7:27     ` Penny Zheng
2021-05-19 20:10       ` Julien Grall
2021-05-20  6:29         ` Penny Zheng

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