Re: possible Malta 4Kc cache problem ...

["Kevin D. Kissell" <kevink@mips.com>]

I think that Carsten's patch (or equivalent) should certainly be
applied to the main tree, but I wonder how relevant it is here.
The flushes associated with trampolines don't do indexed
flush operations, do they?  I don't have a 4Kc platform at
hand, but I think that Jun Sun *may* have found a better
way to get at the other problem I was referring to, which
we rarely saw on non-superscalar issue CPUs, and which
seems to be masked by an otherwise superfluous flush of 
the Icache that was added to the latest versions of break_cow().
If Carsten's patch solves the problem without applying that
other update, I'd want to know that.  If it *doesn't*, I'd be
really interested to know if, by any chance, there is a
corelation between failures of Jun Sun's test and the incidence
of page faults on the CACHE op in protected_icache_invalidate_line().

            Kevin K.

----- Original Message ----- 
From: "Carsten Langgaard" <carstenl@mips.com>
To: "Kevin D. Kissell" <kevink@mips.com>; <linux-mips@linux-mips.org>; "Jun Sun" <jsun@mvista.com>
Sent: Wednesday, December 04, 2002 12:21 PM
Subject: Re: possible Malta 4Kc cache problem ...


> I just noticed that the patch I send (I don't know how long ago), hasn't made it
> into the CVS tree.
> So there is a potentially hole in the indexed flushes, which might only flush one
> of the cache ways.
> 
> Please try the mips32_cache.h, I have attached.
> 
> /Carsten
> 
> 
> 
> Carsten Langgaard wrote:
> 
> > I have just tried your test on a 4Kc and I see no problems.
> > However I'm running on our internal kernel sources, and as Kevin mention we have
> > changed a fixed a few things in this area.
> > As Kevin also mention it sure look more like a I-cache invalidation problem,
> > rather than a D-cache flush problem, as the 4Kc has a write-through cache.
> > One think you could try, is our latest kernel release. You can find it here:
> > ftp://ftp.mips.com/pub/linux/mips/kernel/2.4/images/
> >
> > /Carsten
> >
> > "Kevin D. Kissell" wrote:
> >
> > > > I attached the test case.  Untar it.  Type 'make' and run 'a.out'.
> > > >
> > > > If the test fails you will see a print-out.  Otherwise you see nothing.
> > > >
> > > > It does not always fail.  But if it fails, it is usually pretty consistent.
> > > > Try a few times.  Moving source tree to a different directory may cause
> > > > the symptom appear or disappear.
> > > >
> > > > I spent quite some time to trace this problem, and came to suspect
> > > > there might be a hardware problem.
> > > >
> > > > The problem involves emulating a "lw" instruction in cp1 branch delay
> > > > slot, which needs to  set up trampoline in user stack.  The net effect
> > > > looks as if the icache line or dcache line is not flushed properly.
> > > >
> > > > Using gdb/kgdb, printf or printk in any useful places would hide the bug.
> > > >
> > > > I did find a smaller part of the problem.  flush_cache_sigtramp for
> > > > MIPS32 (4Kc) calls protected_writeback_dcache_line in mips32_cache.h.
> > > > It uses Hit_Writeback_D, and the 4Kc mannual says it is not implemented
> > > > and executed as no-op (*ick*).
> > >
> > > Which version of the 4Kc manual are you looking at?  I'm looking
> > > at a very recent version of the 4Kc Software User's Manual
> > > (version 1.17, dated September 25, 2002), and it only shows
> > > Hit_Writeback_D to be invalid for *secondary and teritary*
> > > caches, which makes sense, since the 4KSc doesn't have any.
> > >
> > > > Even after fixing this, I still see the problem happening.
> > >
> > > That's not too surprising.  The 4Kc D-cache is write-through,
> > > so if you're really seeing a problem with trampolimes, it is almost
> > > certain to be a problem with the Icache invalidation, not the
> > > Dcache flush.
> > >
> > > > If you replace flush_cache_sigtramp() with flush_cache_all(), symptom
> > > > would disppear.
> > >
> > > Which again would make sense if there's a problem on
> > > the icache side of the flush.  Oddly enough, we've seen
> > > some glitches on other CPUs with other kernels that
> > > might have been explicable by failures of protected_flush_icache_line(),
> > > but we never found a problem with it, and a higher-level
> > > memory management patch made the problem go away.
> > > Makes me wonder if we shouldn't look at it again, more
> > > closely.  Is there any possibility that the logic for restarting
> > > a protected kernel access following a page fault will somehow
> > > screw up on CACHE instructions, as opposed to the loads
> > > and stores for which the code was originally written?
> > >
> > > > Several of my tests seem to suggest it is the icache that did not
> > > > get flushed (or updated) properly.
> > > >
> > > > Not re-producible on other MIPS boards.  At least so far.
> > > >
> > > > Does anybody with more knowledge about 4Kc have any clues here?
> > > >
> > > > Thanks.
> > > >
> > > > Jun
> >
> > --
> > _    _ ____  ___   Carsten Langgaard  Mailto:carstenl@mips.com
> > |\  /|||___)(___   MIPS Denmark        Direct: +45 4486 5527
> > | \/ |||    ____)  Lautrupvang 4B      Switch: +45 4486 5555
> >   TECHNOLOGIES     2750 Ballerup       Fax...: +45 4486 5556
> >                    Denmark            http://www.mips.com
> 
> --
> _    _ ____  ___   Carsten Langgaard   Mailto:carstenl@mips.com
> |\  /|||___)(___   MIPS Denmark        Direct: +45 4486 5527
> | \/ |||    ____)  Lautrupvang 4B      Switch: +45 4486 5555
>   TECHNOLOGIES     2750 Ballerup       Fax...: +45 4486 5556
>                    Denmark             http://www.mips.com
> 
> 
> 


--------------------------------------------------------------------------------


> /*
>  * mips32_cache.h
>  *
>  * Carsten Langgaard, carstenl@mips.com
>  * Copyright (C) 2000 MIPS Technologies, Inc.  All rights reserved.
>  *
>  * ########################################################################
>  *
>  *  This program is free software; you can distribute it and/or modify it
>  *  under the terms of the GNU General Public License (Version 2) as
>  *  published by the Free Software Foundation.
>  *
>  *  This program is distributed in the hope it will be useful, but WITHOUT
>  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
>  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
>  *  for more details.
>  *
>  *  You should have received a copy of the GNU General Public License along
>  *  with this program; if not, write to the Free Software Foundation, Inc.,
>  *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
>  *
>  * ########################################################################
>  *
>  * Inline assembly cache operations.
>  * 
>  * This file is the original r4cache.c file with modification that makes the
>  * cache handling more generic.
>  *
>  * FIXME: Handle split L2 caches.
>  *
>  */
> #ifndef _MIPS_R4KCACHE_H
> #define _MIPS_R4KCACHE_H
> 
> #include <asm/asm.h>
> #include <asm/cacheops.h>
> 
> static inline void flush_icache_line_indexed(unsigned long addr)
> {
> unsigned long waystep = icache_size/mips_cpu.icache.ways;
> unsigned int way;
> 
> for (way = 0; way < mips_cpu.icache.ways; way++)
> {
> __asm__ __volatile__(
> ".set noreorder\n\t"
> ".set mips3\n\t"
> "cache %1, (%0)\n\t"
> ".set mips0\n\t"
> ".set reorder"
> :
> : "r" (addr),
> "i" (Index_Invalidate_I));
> 
> addr += waystep;
> }
> }
> 
> static inline void flush_dcache_line_indexed(unsigned long addr)
> {
> unsigned long waystep = dcache_size/mips_cpu.dcache.ways;
> unsigned int way;
> 
> for (way = 0; way < mips_cpu.dcache.ways; way++)
> {
> __asm__ __volatile__(
> ".set noreorder\n\t"
> ".set mips3\n\t"
> "cache %1, (%0)\n\t"
> ".set mips0\n\t"
> ".set reorder"
> :
> : "r" (addr),
> "i" (Index_Writeback_Inv_D));
> 
> addr += waystep;
> }
> }
> 
> static inline void flush_scache_line_indexed(unsigned long addr)
> {
> unsigned long waystep = scache_size/mips_cpu.scache.ways;
> unsigned int way;
> 
> for (way = 0; way < mips_cpu.scache.ways; way++)
> {
> __asm__ __volatile__(
> ".set noreorder\n\t"
> ".set mips3\n\t"
> "cache %1, (%0)\n\t"
> ".set mips0\n\t"
> ".set reorder"
> :
> : "r" (addr),
> "i" (Index_Writeback_Inv_SD));
> 
> addr += waystep;
> }
> }
> 
> static inline void flush_icache_line(unsigned long addr)
> {
> __asm__ __volatile__(
> ".set noreorder\n\t"
> ".set mips3\n\t"
> "cache %1, (%0)\n\t"
> ".set mips0\n\t"
> ".set reorder"
> :
> : "r" (addr),
>   "i" (Hit_Invalidate_I));
> }
> 
> static inline void flush_dcache_line(unsigned long addr)
> {
> __asm__ __volatile__(
> ".set noreorder\n\t"
> ".set mips3\n\t"
> "cache %1, (%0)\n\t"
> ".set mips0\n\t"
> ".set reorder"
> :
> : "r" (addr),
>   "i" (Hit_Writeback_Inv_D));
> }
> 
> static inline void invalidate_dcache_line(unsigned long addr)
> {
> __asm__ __volatile__(
> ".set noreorder\n\t"
> ".set mips3\n\t"
> "cache %1, (%0)\n\t"
> ".set mips0\n\t"
> ".set reorder"
> :
> : "r" (addr),
>   "i" (Hit_Invalidate_D));
> }
> 
> static inline void invalidate_scache_line(unsigned long addr)
> {
> __asm__ __volatile__(
> ".set noreorder\n\t"
> ".set mips3\n\t"
> "cache %1, (%0)\n\t"
> ".set mips0\n\t"
> ".set reorder"
> :
> : "r" (addr),
>   "i" (Hit_Invalidate_SD));
> }
> 
> static inline void flush_scache_line(unsigned long addr)
> {
> __asm__ __volatile__(
> ".set noreorder\n\t"
> ".set mips3\n\t"
> "cache %1, (%0)\n\t"
> ".set mips0\n\t"
> ".set reorder"
> :
> : "r" (addr),
>   "i" (Hit_Writeback_Inv_SD));
> }
> 
> /*
>  * The next two are for badland addresses like signal trampolines.
>  */
> static inline void protected_flush_icache_line(unsigned long addr)
> {
> __asm__ __volatile__(
> ".set noreorder\n\t"
> ".set mips3\n"
> "1:\tcache %1,(%0)\n"
> "2:\t.set mips0\n\t"
> ".set reorder\n\t"
> ".section\t__ex_table,\"a\"\n\t"
> STR(PTR)"\t1b,2b\n\t"
> ".previous"
> :
> : "r" (addr),
>   "i" (Hit_Invalidate_I));
> }
> 
> static inline void protected_writeback_dcache_line(unsigned long addr)
> {
> __asm__ __volatile__(
> ".set noreorder\n\t"
> ".set mips3\n"
> "1:\tcache %1,(%0)\n"
> "2:\t.set mips0\n\t"
> ".set reorder\n\t"
> ".section\t__ex_table,\"a\"\n\t"
> STR(PTR)"\t1b,2b\n\t"
> ".previous"
> :
> : "r" (addr),
>   "i" (Hit_Writeback_D));
> }
> 
> #define cache_unroll(base,op)         \
> __asm__ __volatile__("          \
> .set noreorder;         \
> .set mips3;         \
>                 cache %1, (%0);                 \
> .set mips0; \
> .set reorder" \
> : \
> : "r" (base), \
>   "i" (op));
> 
> 
> static inline void blast_dcache(void)
> {
> unsigned long start = KSEG0;
> unsigned long end = (start + dcache_size);
> 
> while(start < end) {
> cache_unroll(start,Index_Writeback_Inv_D);
> start += dc_lsize;
> }
> }
> 
> static inline void blast_dcache_page(unsigned long page)
> {
> unsigned long start = page;
> unsigned long end = (start + PAGE_SIZE);
> 
> while(start < end) {
> cache_unroll(start,Hit_Writeback_Inv_D);
> start += dc_lsize;
> }
> }
> 
> static inline void blast_dcache_page_indexed(unsigned long page)
> {
> unsigned long start;
> unsigned long end = (page + PAGE_SIZE);
> unsigned long waystep = dcache_size/mips_cpu.dcache.ways;
> unsigned int way;
> 
> for (way = 0; way < mips_cpu.dcache.ways; way++) {
> start = page + way*waystep;
> while(start < end) {
> cache_unroll(start,Index_Writeback_Inv_D);
> start += dc_lsize;
> }
> }
> }
> 
> static inline void blast_icache(void)
> {
> unsigned long start = KSEG0;
> unsigned long end = (start + icache_size);
> 
> while(start < end) {
> cache_unroll(start,Index_Invalidate_I);
> start += ic_lsize;
> }
> }
> 
> static inline void blast_icache_page(unsigned long page)
> {
> unsigned long start = page;
> unsigned long end = (start + PAGE_SIZE);
> 
> while(start < end) {
> cache_unroll(start,Hit_Invalidate_I);
> start += ic_lsize;
> }
> }
> 
> static inline void blast_icache_page_indexed(unsigned long page)
> {
> unsigned long start;
> unsigned long end = (page + PAGE_SIZE);
> unsigned long waystep = icache_size/mips_cpu.icache.ways;
> unsigned int way;
> 
> for (way = 0; way < mips_cpu.icache.ways; way++) {
> start = page + way*waystep;
> while(start < end) {
> cache_unroll(start,Index_Invalidate_I);
> start += ic_lsize;
> }
> }
> }
> 
> static inline void blast_scache(void)
> {
> unsigned long start = KSEG0;
> unsigned long end = KSEG0 + scache_size;
> 
> while(start < end) {
> cache_unroll(start,Index_Writeback_Inv_SD);
> start += sc_lsize;
> }
> }
> 
> static inline void blast_scache_page(unsigned long page)
> {
> unsigned long start = page;
> unsigned long end = page + PAGE_SIZE;
> 
> while(start < end) {
> cache_unroll(start,Hit_Writeback_Inv_SD);
> start += sc_lsize;
> }
> }
> 
> static inline void blast_scache_page_indexed(unsigned long page)
> {
> unsigned long start;
> unsigned long end = (page + PAGE_SIZE);
> unsigned long waystep = scache_size/mips_cpu.scache.ways;
> unsigned int way;
> 
> for (way = 0; way < mips_cpu.scache.ways; way++) {
> start = page + way*waystep;
> while(start < end) {
> cache_unroll(start,Index_Writeback_Inv_SD);
> start += sc_lsize;
> }
> }
> }
> 
> #endif /* !(_MIPS_R4KCACHE_H) */
>