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Date:   Wed, 10 Feb 2021 11:57:40 +1000
From:   Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v5 18/22] powerpc/syscall: Remove FULL_REGS verification
 in system_call_exception
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Michael Ellerman <mpe@ellerman.id.au>, msuchanek@suse.de,
        Paul Mackerras <paulus@samba.org>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <cover.1612796617.git.christophe.leroy@csgroup.eu>
        <6bef4d9ba0cba50160d13e344ee4627ebdf801dc.1612796617.git.christophe.leroy@csgroup.eu>
        <1612836023.l122pe2n2b.astroid@bobo.none>
        <cc1a35a4-07c3-9e64-18d6-57e497f56e33@csgroup.eu>
In-Reply-To: <cc1a35a4-07c3-9e64-18d6-57e497f56e33@csgroup.eu>
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Excerpts from Christophe Leroy's message of February 10, 2021 12:31 am:
>=20
>=20
> Le 09/02/2021 =C3=A0 03:02, Nicholas Piggin a =C3=A9crit=C2=A0:
>> Excerpts from Christophe Leroy's message of February 9, 2021 1:10 am:
>>> For book3s/64, FULL_REGS() is 'true' at all time, so the test voids.
>>> For others, non volatile registers are saved inconditionally.
>>>
>>> So the verification is pointless.
>>>
>>> Should one fail to do it, it would anyway be caught by the
>>> CHECK_FULL_REGS() in copy_thread() as we have removed the
>>> special versions ppc_fork() and friends.
>>>
>>> null_syscall benchmark reduction 4 cycles (332 =3D> 328 cycles)
>>=20
>> I wonder if we rather make a CONFIG option for a bunch of these simpler
>> debug checks here (and also in interrupt exit, wrappers, etc) rather
>> than remove them entirely.
>=20
> We can drop this patch if you prefer. Anyway, like book3s/64, once ppc32 =
also do interrupt=20
> entry/exit in C, FULL_REGS() will already return true.

Sure let's do that.

Thanks,
Nick