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From: Julien Grall <julien@xen.org>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: xen-devel@lists.xenproject.org, Wei.Chen@arm.com,
	Henry.Wang@arm.com, Penny.Zheng@arm.com,
	Bertrand.Marquis@arm.com, Julien Grall <julien.grall@arm.com>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>,
	Julien Grall <jgrall@amazon.com>
Subject: Re: [PATCH RFCv2 14/15] xen/arm: mm: Rework setup_xenheap_mappings()
Date: Sat, 15 May 2021 10:21:15 +0100	[thread overview]
Message-ID: <8cda6d2d-7f3c-fef6-c534-2fadabed1bad@xen.org> (raw)
In-Reply-To: <alpine.DEB.2.21.2105141646340.14426@sstabellini-ThinkPad-T480s>

Hi,

On 15/05/2021 00:51, Stefano Stabellini wrote:
> On Sun, 25 Apr 2021, Julien Grall wrote:
>> From: Julien Grall <julien.grall@arm.com>
>>
>> A few issues have been reported with setup_xenheap_mappings() over the
>> last couple of years. The main ones are:
>>      - It will break on platform supporting more than 512GB of RAM
>>        because the memory allocated by the boot allocator is not yet
>>        mapped.
>>      - Aligning all the regions to 1GB may lead to unexpected result
>>        because we may alias non-cacheable region (such as device or reserved
>>        regions).
>>
>> map_pages_to_xen() was recently reworked to allow superpage mappings and
>> deal with the use of page-tables before they are mapped.
>>
>> Most of the code in setup_xenheap_mappings() is now replaced with a
>> single call to map_pages_to_xen().
>>
>> This also require to re-order the steps setup_mm() so the regions are
>> given to the boot allocator first and then we setup the xenheap
>> mappings.
> 
> I know this is paranoia but doesn't this introduce a requirement on the
> size of the first bank in bootinfo.mem.bank[] ?
> 
> It should be at least 8KB?

AFAIK, the current requirement is 4KB because of the 1GB mapping. Long 
term, it would be 8KB.

> 
> I know it is unlikely but it is theoretically possible to have a first
> bank of just 1KB.

All the page allocators are working at the page granularity level. I am 
not entirely sure whether the current Xen would ignore the region or break.

Note that setup_xenheap_mappings() is taking a base MFN and a number of 
pages to map. So this doesn't look to be a new problem here.

For the 8KB requirement, we can look at first all the pages to the boot 
allocator and then do the mapping.

> 
> I think we should write the requirement down with an in-code comment?
> Or better maybe we should write a message about it in the panic below?

I can write an in-code comment but I think writing down in the panic() 
would be wrong because there is no promise this is going to be the only 
reason it fails (imagine there is a bug in the code...).

Cheers,

-- 
Julien Grall


  reply	other threads:[~2021-05-15  9:21 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-25 20:13 [PATCH RFCv2 00/15] xen/arm: mm: Remove open-coding mappings Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 01/15] xen/arm: lpae: Rename LPAE_ENTRIES_MASK_GS to LPAE_ENTRY_MASK_GS Julien Grall
2021-05-11 22:12   ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 02/15] xen/arm: lpae: Use the generic helpers to defined the Xen PT helpers Julien Grall
2021-05-11 22:26   ` Stefano Stabellini
2021-05-12 14:26     ` Julien Grall
2021-05-12 21:30       ` Stefano Stabellini
2021-05-12 22:16         ` Julien Grall
2021-05-13 22:44           ` Stefano Stabellini
2021-07-03 17:32             ` Julien Grall
2021-07-13 20:53               ` Stefano Stabellini
2021-07-14 17:40                 ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 03/15] xen/arm: p2m: Replace level_{orders, masks} arrays with LEVEL_{ORDER, MASK} Julien Grall
2021-05-11 22:33   ` Stefano Stabellini
2021-05-12 14:39     ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 04/15] xen/arm: mm: Allow other mapping size in xen_pt_update_entry() Julien Grall
2021-05-11 22:42   ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 05/15] xen/arm: mm: Avoid flushing the TLBs when mapping are inserted Julien Grall
2021-05-11 22:51   ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 06/15] xen/arm: mm: Don't open-code Xen PT update in remove_early_mappings() Julien Grall
2021-05-11 22:58   ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 07/15] xen/arm: mm: Re-implement early_fdt_map() using map_pages_to_xen() Julien Grall
2021-05-12 21:41   ` Stefano Stabellini
2021-05-12 22:18     ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 08/15] xen/arm32: mm: Check if the virtual address is shared before updating it Julien Grall
2021-05-12 22:00   ` Stefano Stabellini
2021-05-12 22:23     ` Julien Grall
2021-05-13 22:32       ` Stefano Stabellini
2021-05-13 22:59         ` Julien Grall
2021-05-14  1:04           ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 09/15] xen/arm32: mm: Re-implement setup_xenheap_mappings() using map_pages_to_xen() Julien Grall
2021-05-12 22:07   ` Stefano Stabellini
2021-05-13 17:55     ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 10/15] xen/arm: mm: Allocate xen page tables in domheap rather than xenheap Julien Grall
2021-05-12 22:44   ` Stefano Stabellini
2021-05-13 18:09     ` Julien Grall
2021-05-13 22:27       ` Stefano Stabellini
2021-05-15  8:48         ` Julien Grall
2021-05-18  0:37           ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 11/15] xen/arm: mm: Allow page-table allocation from the boot allocator Julien Grall
2021-05-13 22:58   ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 12/15] xen/arm: add Persistent Map (PMAP) infrastructure Julien Grall
2021-04-26  9:41   ` Xia, Hongyan
2021-07-03 17:57     ` Julien Grall
2021-04-28 21:47   ` Wei Liu
2021-05-14 23:25   ` Stefano Stabellini
2021-05-15  8:54     ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 13/15] xen/arm: mm: Use the PMAP helpers in xen_{,un}map_table() Julien Grall
2021-05-14 23:35   ` Stefano Stabellini
2021-05-15  9:03     ` Julien Grall
2021-04-25 20:13 ` [PATCH RFCv2 14/15] xen/arm: mm: Rework setup_xenheap_mappings() Julien Grall
2021-05-14 23:51   ` Stefano Stabellini
2021-05-15  9:21     ` Julien Grall [this message]
2021-05-18  0:50       ` Stefano Stabellini
2021-04-25 20:13 ` [PATCH RFCv2 15/15] xen/arm: mm: Re-implement setup_frame_table_mappings() with map_pages_to_xen() Julien Grall
2021-05-15  0:02   ` Stefano Stabellini
2021-05-15  9:25     ` Julien Grall
2021-05-18  0:51       ` Stefano Stabellini

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