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SubjectRe: [PATCH v3 19/22] arm64: capabilities: Handle shared entries
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On 12/02/18 17:17, Dave Martin wrote:
> On Fri, Feb 09, 2018 at 05:55:08PM +0000, Suzuki K Poulose wrote:
>> Some capabilities have different criteria for detection and associated
>> actions based on the matching criteria, even though they all share the
>> same capability bit. So far we have used multiple entries with the same
>> capability bit to handle this. This is prone to errors, as the
>> cpu_enable is invoked for each entry, irrespective of whether the
>> detection rule applies to the CPU or not. And also this complicates
>> other helpers, e.g, __this_cpu_has_cap.
>>
>> This patch adds a wrapper entry to cover all the possible variations
>> of a capability by maintaining list of matches + cpu_enable callbacks.
>> To avoid complicating the prototypes for the "matches()", we use
>> arm64_cpu_capabilities maintain the list and we ignore all the other
>> fields except the matches & cpu_enable.
>>
>> This ensures :
>>
>> 1) The capabilitiy is set when at least one of the entry detects
>> 2) Action is only taken for the entries that "matches".
>>
>> This avoids explicit checks in the cpu_enable() take some action.
>> The only constraint here is that, all the entries should have the
>> same "type" (i.e, scope and conflict rules).
>>
>> If a cpu_enable() method is associated with multiple matches for a
>> single capability, care should be taken that either the match criteria
>> are mutually exclusive, or that the method is robust against being
>> called multiple times.
>>
>> This also reverts the changes introduced by commit 67948af41f2e6818ed
>> ("arm64: capabilities: Handle duplicate entries for a capability").
>>
>> Cc: Dave Martin <dave.martin@arm.com>
>> Cc: Robin Murphy <robin.murphy@arm.com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> ---
>> arch/arm64/include/asm/cpufeature.h | 11 ++++++++
>> arch/arm64/kernel/cpu_errata.c | 53 ++++++++++++++++++++++++++++++++-----
>> arch/arm64/kernel/cpufeature.c | 10 +++----
>> 3 files changed, 61 insertions(+), 13 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
>> index 3ab1c3422f14..074537acc08b 100644
>> --- a/arch/arm64/include/asm/cpufeature.h
>> +++ b/arch/arm64/include/asm/cpufeature.h
>> @@ -306,6 +306,17 @@ struct arm64_cpu_capabilities {
>> bool sign;
>> unsigned long hwcap;
>> };
>> + /*
>> + * A list of "matches/cpu_enable" pair for the same "capability"
>> + * of the same "type" as described by the parent. All the
>> + * fields, except "matches"/"cpu_enable" are ignored in the list.
>
> Nit: This is not quite true: other fields may be needed, for use by the
> matches() method -- for example, if matches == has_cpuid_feature, then
> sys_reg, field_pos etc. will be used.
>
> To keep things simple, maybe say "Only matches(), cpu_enable() and
> fields relevant to these methods are significant in the list." ?

Will fix it.

>
>> + * The cpu_enable is invoked only if the corresponding entry
>> + * "matches()". However, if a cpu_enable() method is associated
>> + * with multiple matches, care should be taken that either the
>> + * match criteria are mutually exclusive, or that the method is
>> + * robust against being called multiple times.
>> + */
>> + const struct arm64_cpu_capabilities *cap_list;
>
> Nit: this is not really a list of capabilities, as noted above.
>
> Can we call it something like "match_list"?

Ok.

>
>> };
>> };
>>
>> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
>> index a602a3049404..902d281ea26f 100644
>> --- a/arch/arm64/kernel/cpu_errata.c
>> +++ b/arch/arm64/kernel/cpu_errata.c
>> @@ -264,6 +264,36 @@ qcom_enable_link_stack_sanitization(const struct arm64_cpu_capabilities *entry)
>> .type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM, \
>> CAP_MIDR_RANGE_LIST(midr_list)
>>
>> +/*
>> + * Generic helper for handling capabilties with multiple (match,enable) pairs
>> + * of call backs, sharing the same capability bit.
>> + * Iterate over each entry to see if at least one matches.
>> + */
>> +static bool multi_entry_cap_matches(const struct arm64_cpu_capabilities *entry,
>> + int scope)
>> +{
>> + const struct arm64_cpu_capabilities *caps = entry->cap_list;
>> +
>> + for (; caps->matches; caps++)
>> + if (caps->matches(caps, scope))
>> + return true;
>
> Nit: add blank line?



>> + return false;
>> +}
>> +
>> +/*
>> + * Take appropriate action for all matching entries in the shared capability
>> + * entry.
>> + */
>> +static void multi_entry_cap_cpu_enable(const struct arm64_cpu_capabilities *entry)
>> +{
>> + const struct arm64_cpu_capabilities *caps = entry->cap_list;
>> +
>> + for (; caps->matches; caps++)
>
> Nit: can we move the initialiser into the for(); so
>
> for (entry->cap_list; caps->matches; [...]


>
> IMHO it's more readable to avoid empty expressions in for() unless
> there's a good reason.
>
>> + if (caps->matches(caps, SCOPE_LOCAL_CPU) &&

.capability = ARM64_HARDEN_BP_POST_GUEST_EXIT,
>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>> index 9eb9e9570468..d8663822c604 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -1225,9 +1225,8 @@ static bool __this_cpu_has_cap(const struct arm64_cpu_capabilities *cap_array,
>> return false;
>>
>> for (caps = cap_array; caps->matches; caps++)
>> - if (caps->capability == cap &&
>> - caps->matches(caps, SCOPE_LOCAL_CPU))
>> - return true;
>> + if (caps->capability == cap)
>> + return caps->matches(caps, SCOPE_LOCAL_CPU);
>
> Nit: add blank line?
>
>> return false;

>
> With fair consideration to the nits above,

Will do

>
> Reviewed-by: Dave Martin <Dave.Martin@arm.com>

Thanks
Suzuki
>

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