Re: [Xen-devel] [PATCH] xen/arm64: disable alignment check

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 28/04/14 11:36, Ian Campbell wrote:
> On Mon, 2014-04-28 at 11:24 +0100, David Vrabel wrote:
>> On 28/04/14 10:48, Ian Campbell wrote:
>>> On Sun, 2014-04-27 at 10:10 +0100, Vladimir Murzin wrote:
>>>> Alignment check is enabled by default at Xen boot.
>>>
>>> This has already been disabled in the development branch via:
>>> commit 58bbe7d71239db508c30099bf7b6db7c458f3336
>>> Author: Ian Campbell <ian.campbell@xxxxxxxxxx>
>>> Date:   Wed Mar 26 13:38:45 2014 +0000
>>>
>>>     xen: arm64: disable alignment traps
>>>     
>>>     The mem* primitives which I am about to import from Linux in a 
>>> subsequent
>>>     patch rely on the hardware handling misalignment.
>>>     
>>>     The benefits of an optimised memcpy etc outweigh the downsides.
>>>     
>>>     Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
>>>     Acked-by: Julien Grall <julien.grall@xxxxxxxxxx>
>>>     Acked-by: Tim Deegan <tim@xxxxxxx>
>>>
>>> I will consider this for backport, but first I'd like to consider
>>> whether we shouldn't fix the hypervisor side evtchn FIFO code along the
>>> same lines as the kernel side. David, any thoughts?
>>
>> I believe Jan suggested making Xen's bitops handle 32-bit alignment or
>> adding a new set of 32-bit bitops.
> 
> This is already the case for the arm64 bitops, we deliberately diverged
> from Linux here because there are a bunch of other "misaligned" 4-byte
> bitmasks (one in the malloc implementation springs to mind).

Then I'm not sure what it is you're trying to fix in Xen?

David

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