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Re: [PATCH v4 6/6] xen/arm: mpu: Implement a dummy enable_secondary_cpu_mm


  • To: Ayan Kumar Halder <ayankuma@xxxxxxx>, Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Tue, 29 Oct 2024 09:08:38 +0100
  • Autocrypt: addr=jbeulich@xxxxxxxx; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL
  • Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Tue, 29 Oct 2024 08:08:52 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 28.10.2024 18:38, Ayan Kumar Halder wrote:
> On 28/10/2024 15:01, Jan Beulich wrote:
>> On 28.10.2024 15:39, Ayan Kumar Halder wrote:
>>> On 28/10/2024 12:55, Jan Beulich wrote:
>>>> On 28.10.2024 13:45, Ayan Kumar Halder wrote:
>>>>> --- a/xen/arch/Kconfig
>>>>> +++ b/xen/arch/Kconfig
>>>>> @@ -6,11 +6,13 @@ config PHYS_ADDR_T_32
>>>>>    
>>>>>    config NR_CPUS
>>>>>           int "Maximum number of CPUs"
>>>>> + range 1 1 if ARM && MPU
>>>>>           range 1 16383
>>>>>           default "256" if X86
>>>>>           default "8" if ARM && RCAR3
>>>>>           default "4" if ARM && QEMU
>>>>>           default "4" if ARM && MPSOC
>>>>> + default "1" if ARM && MPU
>>>>>           default "128" if ARM
>>>>>           help
>>>>>             Controls the build-time size of various arrays and bitmaps
>>>> I'm afraid I can't easily tell whether MPU can be used together with any of
>>>> RCAR3, QEMU, or MPSOC. If it can, the new default line would need to move
>>>> up, as it's the first one that has a match on its condition which is being
>>>> used.
>>> MPU cannot be used with any of the existing platforms.
>> That is - qemu can't emulate such an environment, i.e. even QEMU and MPU
>> don't go together?
> 
> Qemu has support for Aarch32 MPU at EL2 and EL1 (ie R52). As far as I am 
> aware, there is no support for Aarch64 MPU in Qemu (ie R82).
> 
> Even for R52, I could not get the upstream Qemu working (emulating some 
> Arm reference platform).
> 
> I could get the Xilinx fork of Qemu (https://github.com/Xilinx/qemu) 
> working which emulates AMD's SoC using R52.
> 
> However, this should not impact the current patch. There is no Qemu in 
> xen/arch/arm/platforms/*.

Aiui that's not relevant. There is a QEMU item in 
xen/arch/arm/platforms/Kconfig.
I continue to fail to see why that couldn't be selected together with MPU. Yet 
if
it can be, you'd end up with a default of 4, not 1, if it actually _is_ 
selected.
Alternatively QEMU (and maybe also RCAR3 and MPSOC) need to be mutually 
exclusive
with MPU. Hmm, looks like that's already the case, by patch 2 suppressing the
"Platform Support" prompt. While that looks fragile to me, I'm sorry for the
noise then.

Jan



 


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