Re: [Xen-devel] [PATCH] xen/arm64: Fix incorrect memory region size in TCR2_EL2

[Shanker Donthineni <shankerd@xxxxxxxxxxxxxx>]

HI Jullen,

On 03/12/2016 07:13 AM, Julien Grall wrote:
> Hi Shanker,
>
> On 11/03/2016 04:28, Shanker Donthineni wrote:
>> The maximum and minimum values for T0SZ depend on level of
>> translation as per AArch64 Virtual Memory System Architecture.
>> The current code sets T0SZ to zero in TCR2_EL2 which is not
>
> s/TCR2_EL2/TCR_EL2/
>

Sorry for typo, I will fix in next patch

>> valid and also might see unexpected behavior on some CPUs.
>
> Can you provide more details?
>

We are not able to boot XEN on Qualcomm platforms and CPU hung after
after executing this line of ASM code.

> I looked at the specification, programming the field T0SZ to 0 is valid
> (see D4-1463 ARM DDI 0487A.b):
>
> "For a stage 1 translation
> The minimum TxSZ value is 16. If TxSZ is programmed to a value smaller
> than 16 then the implementation behaves as if the field were programmed
> to 16 for all purposes other than reading back the value of the field."
>

The behavior of T0SZ=0 is described in ARM spec (DDI0487A_h, page 1752). Still 
I think setting
the T0SZ to 48bit is the right fix similar to LINUX KVM64 EL2 code.

For a stage 1 translation
The minimum TxSZ value is 16. If TxSZ is programmed to a value smaller than 16 
then it is
IMPLEMENTATION DEFINED whether:

• The implementation behaves as if the field were programmed to 16 for all 
purposes other than
reading back the value of the field.

• Any use of the TxSZ value generates a stage 1 Level 0 Translation fault.


>> This patch sets T0SZ to (64-48)bits since XEN uses all 4 levels
>> to cover 48bit (256TB) virtual address space.
>>
>> Signed-off-by: Shanker Donthineni <shankerd@xxxxxxxxxxxxxx>
>> ---
>>   xen/arch/arm/arm64/head.S | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
>> index 19fa2bb..28ee404 100644
>> --- a/xen/arch/arm/arm64/head.S
>> +++ b/xen/arch/arm/arm64/head.S
>> @@ -343,7 +343,7 @@ skip_bss:
>>            * PT walks use Inner-Shareable accesses,
>>            * PT walks are write-back, write-allocate in both cache levels,
>>            * Full 64-bit address space goes through this table. */
>
> This comment is no longer valid with your changes. Please update it.
>

Sure, I will change to 48bit virtual address space.
>> -        ldr   x0, 
>> =(TCR_RES1|TCR_SH0_IS|TCR_ORGN0_WBWA|TCR_IRGN0_WBWA|TCR_T0SZ(0))
>> +        ldr   x0, 
>> =(TCR_RES1|TCR_SH0_IS|TCR_ORGN0_WBWA|TCR_IRGN0_WBWA|TCR_T0SZ(64-48))
>>           /* ID_AA64MMFR0_EL1[3:0] (PARange) corresponds to TCR_EL2[18:16] 
>> (PS) */
>>           mrs   x1, ID_AA64MMFR0_EL1
>>           bfi   x0, x1, #16, #3
>>
>
> Regards,
>

-- 
Shanker Donthineni
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux 
Foundation Collaborative Project


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