linux-kernel - Re: [4.1,013/123] MIPS: c-r4k: Fix cache flushing for MT cores

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Message-ID: <20150810184953.GA19646@kroah.com>
Date:	Mon, 10 Aug 2015 11:49:53 -0700
From:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Markos Chandras <markos.chandras@...tec.com>,
	linux-mips@...ux-mips.org, Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [4.1,013/123] MIPS: c-r4k: Fix cache flushing for MT cores

On Mon, Aug 10, 2015 at 11:36:34AM -0700, Leonid Yegoshin wrote:
> On 08/08/2015 03:08 PM, gregkh@...uxfoundation.org wrote:
> >4.1-stable review patch.  If anyone has any objections, please let me know.
> >
> >
> Yes, I have objection. Please look into excepts from my mail exchange with
> Markos:
> 
> >On 06/25/2015 03:59 AM, Markos Chandras wrote:
> >
> >>@@ -51,9 +51,8 @@ static inline void r4k_on_each_cpu(void (*func) (void *info), void *info)
> >>  {
> >>  	preempt_disable();
> >>-#ifndef CONFIG_MIPS_MT_SMP
> >>-	smp_call_function(func, info, 1);
> >>-#endif
> >>+	if (config_enabled(CONFIG_SMP))
> >>+		smp_call_function_many(&cpu_foreign_map, func, info, 1);
> >>  	func(info);
> >>  	preempt_enable();
> >>  }
> >
> >You can NOT do this because r4k_on_each_cpu() is still used for
> >non-MIPS/IMG processors for SAFE INDEX cache flushes -
> >cpu_has_safe_index_cacheops (it is not safe in CM/CM2/CM3 environment).
> >
> >
> >And a little explanation and history:
> >
> >The function r4k_on_each_cpu() can NOT be used simultaneously for index
> >cacheops and address cacheops because both have a different rules in
> >applying in other cores and that is different in inter-core HW blocks of
> >various vendors. CM propogates address cacheops from core-to-core (no IPI
> >calls are needed) but another vendors may do not - this is indicated by
> >CONFIG_MIPS_MT_SMP (and a dropped now CONFIG_MIPS_MT_SMTC).
> >
> >Unfortunately, before 2.6.35.9 this function was used for index cacheops
> >too in any kernel and that is WRONG, at least for CM-based systems.
> >So, I splitted index and address cacheops and wrote a functions
> >r4k_indexop_on_each_cpu and put it in use in at least in dlm-2.6.35.9 and
> >it finally made a way to dev-linux-mti-3.6. This is a famous patch named:
> >
> >    MIPS: Cache flush functions are reworked.
> >
> >    This patch is a preparation for EVA support in kernel.
> >
> >    However, it also fixes a bug then index cacheop was not ran
> >    on multiple CPUs with unsafe index cacheops (flush_cache_vmap,
> >    flush_icache_range, flush_cache_range, __flush_cache_all).
> >
> >    Additionally, it optimizes a usage of index and address cacheops for
> >    address range flushes depending from address range size.
> >
> >    Because of that reasons it is a separate patch from EVA support.
> >
> >    Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
> >    Signed-off-by: Steven J. Hill <Steven.Hill@...tec.com>
> >    (cherry picked from commit 6b05dd71da1136fbad0ce642790c4c99343f05e7)
> >
> 
> (history is skipped)
> 
> Note: the replacement of
> 
>     if (config_enabled(CONFIG_SMP))
> 
> to
> if (!mips_cm_present())
> 
> doesn't solve a problem - in CM-based environment the index cache ops MUST
> be delivered to other core via IPI.

So, this is broken in Linus's tree too?  Or is it fixed there, and if
so, what is the git commit id?

thanks,

greg k-h
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