Re: [Xen-devel] [PATCH 01/18] xen/arm: Introduce a helper to get default HCR_EL2 flags

[Wei Chen <Wei.Chen@xxxxxxx>]

Hi Julien,

On 2017/3/15 19:01, Julien Grall wrote:
> On 15/03/17 07:19, Wei Chen wrote:
>> Hi Stefano,
>
> Hello,
>
>> On 2017/3/15 8:24, Stefano Stabellini wrote:
>>> On Mon, 13 Mar 2017, Wei Chen wrote:
>>>> We want to add HCR_EL2 register to Xen context switch. And each copy
>>>> of HCR_EL2 in vcpu structure will be initialized with the same set
>>>> of trap flags as the HCR_EL2 register. We introduce a helper here to
>>>> represent these flags to be reused easily.
>>>>
>>>> Signed-off-by: Wei Chen <Wei.Chen@xxxxxxx>
>>>> ---
>>>>  xen/arch/arm/traps.c            | 11 ++++++++---
>>>>  xen/include/asm-arm/processor.h |  2 ++
>>>>  2 files changed, 10 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
>>>> index 614501f..d343c66 100644
>>>> --- a/xen/arch/arm/traps.c
>>>> +++ b/xen/arch/arm/traps.c
>>>> @@ -115,6 +115,13 @@ static void __init parse_vwfi(const char *s)
>>>>  }
>>>>  custom_param("vwfi", parse_vwfi);
>>>>
>>>> +register_t get_default_hcr_flags(void)
>>>> +{
>>>> +    return  (HCR_PTW|HCR_BSU_INNER|HCR_AMO|HCR_IMO|HCR_FMO|HCR_VM|
>>>> +             (vwfi != NATIVE ? (HCR_TWI|HCR_TWE) : 0) |
>>>> +             HCR_TSC|HCR_TAC|HCR_SWIO|HCR_TIDCP|HCR_FB);
>>>> +}
>>>
>>> I haven't finished reading this series yet, but I would make this a
>>> static inline function if possible
>>>
>>
>> I had considered to use static inline before. But it must move the
>>
>> static enum {
>>         TRAP,
>>         NATIVE,
>> } vwfi;
>>
>> to the header file at the same time. But get_default_hcr_flags would
>> not be used frequently. So I thought it didn't have enough value to
>> change a less relevant code to make this function become static inline.
>
> Looking at the spec, HCR_EL2 is controlling the behavior of the VM. We
> only need to ensure this to be set before going to EL1/EL0. Note that
> the reset value of some register are architecturally UNKNOWN, but I
> don't think we care here.
>
> So I would suggest to drop the setting in init_traps and only rely on
> the one in when returning to the guest. And therefore this function
> could be moved in domain.c
>
> Any opinions?
>

It seems good. I will do some test, if everything pass, I will do this
change in next version.

> Cheers,
>


-- 
Regards,
Wei Chen

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