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
next prev parent reply other threads:[~2021-05-15 9:21 UTC|newest]
Thread overview: 59+ 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
2022-02-12 19:16 ` Julien Grall
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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