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SubjectRe: [PATCH v2 11/20] arm64: capabilities: Add support for features enabled early
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On 08/02/18 11:35, Dave Martin wrote:
> On Wed, Feb 07, 2018 at 06:34:37PM +0000, Suzuki K Poulose wrote:
>> On 07/02/18 10:38, Dave Martin wrote:
>>> On Wed, Jan 31, 2018 at 06:27:58PM +0000, Suzuki K Poulose wrote:

>>>> * 3) Verification: When a CPU is brought online (e.g, by user or by the kernel),
>>>> * the kernel should make sure that it is safe to use the CPU, by verifying
>>>> @@ -139,11 +148,22 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
>>>> *
>>>> * As explained in (2) above, capabilities could be finalised at different
>>>> * points in the execution. Each CPU is verified against the "finalised"
>>>> - * capabilities and if there is a conflict, the kernel takes an action, based
>>>> - * on the severity (e.g, a CPU could be prevented from booting or cause a
>>>> - * kernel panic). The CPU is allowed to "affect" the state of the capability,
>>>> - * if it has not been finalised already. See section 5 for more details on
>>>> - * conflicts.
>>>> + * capabilities.
>>>> + *
>>>> + * x------------------------------------------------------------------- x
>>>> + * | Verification: | Boot CPU | SMP CPUs by kernel | CPUs by user |
>>>> + * |--------------------------------------------------------------------|
>>>> + * | Primary boot CPU | | | |
>>>> + * | capability | n | y | y |
>>>> + * |--------------------------------------------------------------------|
>>>> + * | All others | n | n | y |
>>>> + * x--------------------------------------------------------------------x
>>>
>>> Minor clarify nit: it's not obvious that "n" means "no conflict" and "y"
>>> means "conflict".
>>>
>>> Could we have blank cell versus "X" (with a note saying what that
>>> means), or "ok" versus "CONFLICT"?
>>
>> This is not strictly about conflicts, but about what each CPU get
>> verified against. Since there are multiple stages of "finalisation"
>
> You're right: I meant something like "potential conflict", but I hadn't
> read the previous paragraph carefully enough and didn't explain what I
> meant very well.
>
>> for the capabilities, the table shows how the CPUs get verified.
>>
>> Would it help if I changed the description above the table to :
>>
>> * As explained in (2) above, capabilities could be finalised at different
>> * points in the execution. Each CPU is verified against the "finalised"
>> * capabilities. The following table shows, the capabilities verified
>> * against each CPU in the system.
>> *
>> * x------------------------------------------------------------------- x
>> * | Verified against: | Boot CPU | SMP CPUs by kernel | CPUs by user |
>
> I still find it a bit cryptic.
>
> Would it be simpler just to write this out in prose, with reference to
> the actual capability types? I feel that things have to be abbreviated
> a bit to fit nicely into the table otherwise.
>
> What about:
>
> * As explained in (2) above, capabilities could be finalised at different
> * points in the execution, depending on the capability type. Each newly booted
> * CPU is verified against those capabilities that have been finalised by the
> * time that CPU boots:
> *
> * * SCOPE_BOOT_CPU: all CPUs are verified against the capability except
> * for the primary boot CPU.
> *
> * * SCOPE_LOCAL_CPU, SCOPE_SYSTEM: all CPUs hotplugged on by the user
> * after kernel boot are verified against the capability.

Sure, looks better.

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