Re: [PATCH V4] xen/arm: domain_build: allocate lowmem for dom0 as much as possible

[Peng Fan <van.freenix@gmail.com>]

On Thu, Nov 10, 2016 at 01:01:38PM +0000, Julien Grall wrote:
>(CC Wei as release manager)
>
>On 10/11/16 08:30, Peng Fan wrote:
>>Hi Julien,
>
>Hi Peng,
>
>>On Tue, Nov 01, 2016 at 02:42:06PM +0000, Julien Grall wrote:
>>>Hi Peng,
>>>
>>>Sorry for the late answer.
>>>
>>>On 23/09/2016 03:55, Peng Fan wrote:
>>>>On AArch64 SoCs, some IPs may only have the capability to access
>>>>32 bits address space. The physical memory assigned for Dom0 maybe
>>>>not in 4GB address space, then the IPs will not work properly.
>>>>So need to allocate memory under 4GB for Dom0.
>>>>
>>>>There is no restriction that how much lowmem needs to be allocated for
>>>>Dom0 ,so allocate lowmem as much as possible for Dom0.
>>>>
>>>>This patch does not affect 32-bit domain, because Variable "lowmem" is
>>>>set to true at the beginning. If failed to allocate bank0 under 4GB,
>>>>need to panic for 32-bit domain, because 32-bit domain requires bank0
>>>>be allocated under 4GB.
>>>>
>>>>For 64-bit domain, set "lowmem" to false, and continue allocating
>>>>memory from above 4GB.
>>>>
>>>>Signed-off-by: Peng Fan <peng.fan@nxp.com>
>>>>Cc: Stefano Stabellini <sstabellini@kernel.org>
>>>>Cc: Julien Grall <julien.grall@arm.com>
>>>
>>>Reviewed-by: Julien Grall <julien.grall@arm.com>
>>>
>>>I am undecided whether this should be considered as a bug fix for Xen 4.8.
>>>Are you aware of any ARM64 platform we currently support requiring allocation
>>>of memory below 4GB?
>>
>>I have no idea about this (:, but I think this is a bug fix. Alought current
>>supported platforms works well, users may choose 4.8 to support their
>>new platform which has the limitation to access 64bit address.
>
>We are already late in the release process (rc5) for Xen 4.8. So we need to
>be careful when including a bug fix and evaluate the pros and cons.
>
>This patch is modifying the DOM0 memory layout for all 64-bit platforms. So
>it could potentially break one of the platform we  officially support (see
>[1] for a non-exhaustive list). We don't have a test suite running
>automatically for ARM64 at the moment (it is been working on), this means
>that manual testing needs to be done. I am not aware of any platform, in the
>list we supports, having this issue so I prefer to stay on the safe side and
>defer this patch for Xen 4.9.

Ok. Defer it for 4.9 to avoid breaking any platforms. :)

>
>If a user cares about Xen 4.8 for their platforms, then they could request
>the patch to be backported in Xen 4.8 after the release and after extensive
>testing in staging.

Yeah. Agree

Thanks,
Peng.

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