Re: [Xen-devel] [[PATCH for-4.13]] xen/arm: mm: Allow generic xen page-tables helpers to be called early

From: "Jürgen Groß" <jgross@suse.com>
To: Julien Grall <julien.grall@arm.com>, xen-devel@lists.xenproject.org
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [Xen-devel] [[PATCH for-4.13]] xen/arm: mm: Allow generic xen page-tables helpers to be called early
Date: Wed, 25 Sep 2019 17:27:08 +0200	[thread overview]
Message-ID: <68142dcd-6d4d-926d-0148-55ea0d6db7d6@suse.com> (raw)
In-Reply-To: <5c96e276-4fdb-4879-c162-3f90dbe5021c@arm.com>

On 25.09.19 17:23, Julien Grall wrote:
> Hi,
> 
> I am CCing Juergen to mark this as a blocker for 4.13. Without this 
> patch, Xen cannot be booted using GRUB.
> 
> Cheers,
> 
> On 17/09/2019 17:02, Julien Grall wrote:
>> The current implementations of xen_{map, unmap}_table() expect
>> {map, unmap}_domain_page() to be usable. Those helpers are used to
>> map/unmap page tables while update Xen page-tables.
>>
>> Since commit 022387ee1a "xen/arm: mm: Don't open-code Xen PT update in
>> {set, clear}_fixmap()", setup_fixmap() will make use of the helpers
>> mentioned above. When booting Xen using GRUB, setup_fixmap() may be used
>> before map_domain_page() can be called. This will result to data abort:
>>
>> (XEN) Data Abort Trap. Syndrome=0x5
>> (XEN) CPU0: Unexpected Trap: Data Abort
>>
>> [...]
>>
>> (XEN) Xen call trace:
>> (XEN)    [<000000000025ab6c>] mm.c#xen_pt_update+0x2b4/0x59c (PC)
>> (XEN)    [<000000000025ab20>] mm.c#xen_pt_update+0x268/0x59c (LR)
>> (XEN)    [<000000000025ae70>] set_fixmap+0x1c/0x2c
>> (XEN)    [<00000000002a9c98>] copy_from_paddr+0x7c/0xdc
>> (XEN)    [<00000000002a4ae0>] has_xsm_magic+0x18/0x34
>> (XEN)    [<00000000002a5b5c>] bootfdt.c#early_scan_node+0x398/0x560
>> (XEN)    [<00000000002a5de0>] device_tree_for_each_node+0xbc/0x144
>> (XEN)    [<00000000002a5ed4>] boot_fdt_info+0x6c/0x260
>> (XEN)    [<00000000002ac0d0>] start_xen+0x108/0xc74
>> (XEN)    [<000000000020044c>] arm64/head.o#paging+0x60/0x88
>>
>> During early boot, the page tables are either statically allocated in
>> Xen binary or allocated via alloc_boot_pages().
>>
>> For statically allocated page-tables, they will already be mapped as
>> part of Xen binary. So we can easily find the virtual address.
>>
>> For dynamically allocated page-tables, we need to rely
>> map_domain_page() to be functionally working.
>>
>> For arm32, the call will be usable much before page can be dynamically
>> allocated (see setup_pagetables()). For arm64, the call will be usable
>> after setup_xenheap_mappings().
>>
>> In both cases, memory are given to the boot allocator afterwards. So we
>> can rely on map_domain_page() for mapping page tables allocated
>> dynamically.
>>
>> The helpers xen_{map, unmap}_table() are now updated to take into
>> account the case where page-tables are part of Xen binary.
>>
>> Fixes: 022387ee1a ('xen/arm: mm: Don't open-code Xen PT update in 
>> {set, clear}_fixmap()')
>> Signed-off-by: Julien Grall <julien.grall@arm.com>

Release-acked-by: Juergen Gross <jgross@suse.com>


Juergen

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