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Re: [PATCH] powerpc: Only enable TLE with PPC_FEATURE2_HTM_NOSC


Hi Adhemerval,

On 08/28/2018 08:48 AM, Adhemerval Zanella wrote:
> 
> 
> On 27/08/2018 19:44, Tulio Magno Quites Machado Filho wrote:
>> Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:

<snip>

>> Can't ABORT_TRANSACTION check for PPC_FEATURE2_HTM_NOSC in tcbhead_t.hwcap and
>> continue to support older Linux versions?
>>
> 
> I don't have a strong opinion here, but chatting with Breno I had the impression
> that TLE (and HTM in general) is only used on kernel with this recent fix. This
> patch is really a hack insertion that penalizes all syscall for an specific
> feature which may not be present in the kernel.

In fact, it is more than a penalization (which is also there). The current
design seems to be incoherent with the Kernel design[1] and limiting the
feature usage. By the kernel design, a syscall executed inside a suspended
transaction is allowed, as said by the kernel documentation[1]:

 "Syscalls made from within a suspended transaction are performed as normal and
  the transaction is not explicitly doomed by the kernel"

The statement above becomes invalid if the syscall is performed through glibc
nowadays, which I understand is an undesired behavior.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/powerpc/transactional_memory.txt#n81



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