From: Nicholas Piggin <npiggin@gmail.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 0/9] powerpc: Switch to CONFIG_THREAD_INFO_IN_TASK
Date: Tue, 9 Oct 2018 20:54:30 +1000 [thread overview]
Message-ID: <20181009205430.351134eb@roar.ozlabs.ibm.com> (raw)
In-Reply-To: <df8575fba80d19e6e58c16266350e9980c432ae1.camel@kernel.crashing.org>
On Mon, 08 Oct 2018 20:59:56 +1100
Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
> On Mon, 2018-10-08 at 09:16 +0000, Christophe Leroy wrote:
> > The purpose of this serie is to activate CONFIG_THREAD_INFO_IN_TASK which
> > moves the thread_info into task_struct.
>
> We need to make sure we don't have code that assumes that we don't take
> faults on TI access.
>
> On ppc64, the stack SLB entries are bolted, which means the TI is too.
>
> We might have code that assumes that we don't get SLB faults when
> accessing TI. If not, we're fine but that needs a close look.
Oh, we do. I think the entry side might be okay, but on exit we have
at least one (in syscall and interrupt exit both):
/*
* Disable interrupts so current_thread_info()->flags can't change,
* and so that we don't get interrupted after loading SRR0/1.
*/
#ifdef CONFIG_PPC_BOOK3E
wrteei 0
#else
/*
* For performance reasons we clear RI the same time that we
* clear EE. We only need to clear RI just before we restore r13
* below, but batching it with EE saves us one expensive mtmsrd call.
* We have to be careful to restore RI if we branch anywhere from
* here (eg syscall_exit_work).
*/
li r11,0
mtmsrd r11,1
#endif /* CONFIG_PPC_BOOK3E */
ld r9,TI_FLAGS(r12)
So taking an SLB there will cause an unrecoverable.
I think we can probably get rid of that optimization for now. I've found
for non-trivial syscalls it's often a loss if FP was used. I have a
couple of different options I'm working on to get rid of the mtmsrd
entirely we can go with instead (but I don't think those have to come
before Christophe's patch).
Thanks,
Nick
prev parent reply other threads:[~2018-10-09 10:54 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-08 9:16 [PATCH v6 0/9] powerpc: Switch to CONFIG_THREAD_INFO_IN_TASK Christophe Leroy
2018-10-08 9:16 ` [PATCH v6 1/9] book3s/64: avoid circular header inclusion in mmu-hash.h Christophe Leroy
2018-10-08 9:16 ` [PATCH v6 2/9] powerpc: Only use task_struct 'cpu' field on SMP Christophe Leroy
2018-10-08 9:16 ` [PATCH v6 3/9] powerpc: Prepare for moving thread_info into task_struct Christophe Leroy
2018-10-08 9:16 ` [PATCH v6 4/9] powerpc: Activate CONFIG_THREAD_INFO_IN_TASK Christophe Leroy
2018-10-08 9:16 ` [PATCH v6 5/9] powerpc: regain entire stack space Christophe Leroy
2018-10-08 9:16 ` [PATCH v6 6/9] powerpc: 'current_set' is now a table of task_struct pointers Christophe Leroy
2018-10-08 9:16 ` [PATCH v6 7/9] powerpc/32: Remove CURRENT_THREAD_INFO and rename TI_CPU Christophe Leroy
2018-10-08 9:16 ` [PATCH v6 8/9] powerpc/64: Remove CURRENT_THREAD_INFO Christophe Leroy
2018-10-08 9:16 ` [PATCH v6 9/9] powerpc: clean stack pointers naming Christophe Leroy
2018-10-08 9:59 ` [PATCH v6 0/9] powerpc: Switch to CONFIG_THREAD_INFO_IN_TASK Benjamin Herrenschmidt
2018-10-09 10:54 ` Nicholas Piggin [this message]
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