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[222.152.189.37]) by smtp.gmail.com with ESMTPSA id g11sm7294831pju.13.2021.08.05.20.10.57 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 05 Aug 2021 20:11:00 -0700 (PDT) Subject: Re: RFC: remove set_fs for m68k To: Christoph Hellwig References: <969718aa-92d4-e77b-0630-f9da6c809178@gmail.com> <20210713054134.GA5880@lst.de> <90e30f50-f062-ac8d-68e7-1250c886d0e1@gmail.com> <20210713085419.GA22839@lst.de> <3acb1a9e-9133-50d4-a642-98d7046d6d4f@gmail.com> <65a95ae0-4734-68ce-ef71-7491b5534718@gmail.com> <8f470389-fe8a-90b0-19a5-68f85526b30e@gmail.com> <20210721170529.GA14550@lst.de> <20210723051126.GA31274@lst.de> <8884e940-22e8-72a5-e9ec-f9b2628b6ef4@gmail.com> Cc: Andreas Schwab , Geert Uytterhoeven , Greg Ungerer , linux-m68k@lists.linux-m68k.org, Linus Torvalds From: Michael Schmitz Message-ID: <251aa093-047a-b37c-4e88-d543c6fa8bc6@gmail.com> Date: Fri, 6 Aug 2021 15:10:55 +1200 User-Agent: Mozilla/5.0 (X11; Linux ppc; rv:45.0) Gecko/20100101 Icedove/45.4.0 MIME-Version: 1.0 In-Reply-To: <8884e940-22e8-72a5-e9ec-f9b2628b6ef4@gmail.com> Content-Type: multipart/mixed; boundary="------------3E293333351F33042270B84D" Precedence: bulk List-ID: X-Mailing-List: linux-m68k@vger.kernel.org This is a multi-part message in MIME format. --------------3E293333351F33042270B84D Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Hi Christoph, Am 01.08.2021 um 07:31 schrieb Michael Schmitz: > Hi Christoph, >> I'll back out the top commit of your series (the one removing set_fs()) >> and retest. Again, this may take a few days to show any results. > > No further format errors, kernel panics or lockups seen after almost a > week of tests. > > That suggests something is wrong with your 'm68k: remove set_fs()' commit. > > I'll try adding a get_fc() and warn whenever FC does not match what your > patch expects, maybe that can help to get a clearer picture. See attached patches, to be applied on top of your RFC series - ran this for five days now, with no further errors. Will run this a while longer yet, but in the ordinary course of testing, I'd have seen errors by now. Haven't seen the WARN_ON trigger once yet though, which is more than a little odd. Heisenbug? I am aware that this patch defeats the purpose of the 'lets lose set_fs' patch series, and Linus was quite convincing in saying preemption couldn't be an issue so saving DFC ought not to be necessary. If there is anything else I can try to get to the bottom of these format errors, please say so. Cheers, Michael --------------3E293333351F33042270B84D Content-Type: text/x-diff; name="0002-m68k-warn-in-get_fc-if-DFC-is-not-USER_DATA.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename*0="0002-m68k-warn-in-get_fc-if-DFC-is-not-USER_DATA.patch" >From d5f7c3d4b4e4b437dfb54f9eb1ed6876dfb63744 Mon Sep 17 00:00:00 2001 From: Michael Schmitz Date: Sun, 1 Aug 2021 13:06:21 +1200 Subject: [PATCH 2/2] m68k: warn in get_fc() if DFC is not USER_DATA Trace uacess mode restore operations that mess up the SFC/DFC registers - read out current DFC before changing modes and warn when the current mode wasn't USER_DATA! Signed-off-by: Michael Schmitz --- arch/m68k/include/asm/processor.h | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/m68k/include/asm/processor.h b/arch/m68k/include/asm/processor.h index 29dfa54..a8c533d 100644 --- a/arch/m68k/include/asm/processor.h +++ b/arch/m68k/include/asm/processor.h @@ -98,6 +98,7 @@ static inline unsigned long get_fc(void) { unsigned long val; __asm__ ("movec %/dfc,%0":"=r" (val):); + WARN_ON_ONCE(val != USER_DATA); return val; } /* -- 2.7.4 --------------3E293333351F33042270B84D Content-Type: text/x-diff; name="0001-m68k-add-get_fc-to-read-uaccess-mode.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="0001-m68k-add-get_fc-to-read-uaccess-mode.patch" >From fcb3f2543125ca3fe269b50646f8c4782d31ba80 Mon Sep 17 00:00:00 2001 From: Michael Schmitz Date: Sun, 1 Aug 2021 12:11:59 +1200 Subject: [PATCH 1/2] m68k: add get_fc() to read uaccess mode Add back get_fc(), force_user_fc_begin() and force_user_fc_end(), and use these to restore original DFC after uaccess operations, instead of unconditionally setting USER_DATA. Signed-off-by: Michael Schmitz --- arch/m68k/include/asm/processor.h | 35 +++++++++++++++++++++++++++++++++++ arch/m68k/include/asm/tlbflush.h | 8 ++++++-- arch/m68k/kernel/process.c | 2 +- arch/m68k/kernel/traps.c | 6 ++++-- arch/m68k/mm/cache.c | 4 +++- 5 files changed, 49 insertions(+), 6 deletions(-) diff --git a/arch/m68k/include/asm/processor.h b/arch/m68k/include/asm/processor.h index debb453..29dfa54 100644 --- a/arch/m68k/include/asm/processor.h +++ b/arch/m68k/include/asm/processor.h @@ -94,10 +94,45 @@ static inline void set_fc(unsigned long val) "movec %0,%/dfc\n\t" : /* no outputs */ : "r" (val) : "memory"); } +static inline unsigned long get_fc(void) +{ + unsigned long val; + __asm__ ("movec %/dfc,%0":"=r" (val):); + return val; +} +/* + * Force the uaccess routines to be wired up for actual userspace access, + * overriding any possible set_fs(KERNEL_DS) still lingering around. Undone + * using force_uaccess_end below. + */ +static inline unsigned long force_user_fc_begin(void) +{ + unsigned long fc = get_fc(); + + set_fc(USER_DATA); + return fc; +} + +static inline void force_user_fc_end(unsigned long oldfc) +{ + set_fc(oldfc); +} #else static inline void set_fc(unsigned long val) { } +static inline unsigned long get_fs(void) +{ + return USER_DATA; +} +static inline unsigned long force_user_fc_begin(void) +{ + return USER_DATA; +} + +static inline void force_user_fc_end(unsigned long oldfc) +{ +} #endif /* CONFIG_CPU_HAS_ADDRESS_SPACES */ struct thread_struct { diff --git a/arch/m68k/include/asm/tlbflush.h b/arch/m68k/include/asm/tlbflush.h index 524b13d..7c34d14 100644 --- a/arch/m68k/include/asm/tlbflush.h +++ b/arch/m68k/include/asm/tlbflush.h @@ -13,12 +13,13 @@ static inline void flush_tlb_kernel_page(void *addr) if (CPU_IS_COLDFIRE) { mmu_write(MMUOR, MMUOR_CNL); } else if (CPU_IS_040_OR_060) { + unsigned long old_fc = get_fc(); set_fc(SUPER_DATA); __asm__ __volatile__(".chip 68040\n\t" "pflush (%0)\n\t" ".chip 68k" : : "a" (addr)); - set_fc(USER_DATA); + set_fc(old_fc); } else if (CPU_IS_020_OR_030) __asm__ __volatile__("pflush #4,#4,(%0)" : : "a" (addr)); } @@ -83,8 +84,11 @@ static inline void flush_tlb_mm(struct mm_struct *mm) static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr) { - if (vma->vm_mm == current->active_mm) + if (vma->vm_mm == current->active_mm) { + unsigned long old_fc = force_user_fc_begin(); __flush_tlb_one(addr); + force_user_fc_end(old_fc); + } } static inline void flush_tlb_range(struct vm_area_struct *vma, diff --git a/arch/m68k/kernel/process.c b/arch/m68k/kernel/process.c index fb257b7..cab012d 100644 --- a/arch/m68k/kernel/process.c +++ b/arch/m68k/kernel/process.c @@ -155,7 +155,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp, unsigned long arg, * Must save the current SFC/DFC value, NOT the value when * the parent was last descheduled - RGH 10-08-96 */ - p->thread.fc = USER_DATA; + p->thread.fc = get_fc(); if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) { /* kernel thread */ diff --git a/arch/m68k/kernel/traps.c b/arch/m68k/kernel/traps.c index c5e0a4f..1b07329 100644 --- a/arch/m68k/kernel/traps.c +++ b/arch/m68k/kernel/traps.c @@ -181,6 +181,7 @@ static inline void access_error060 (struct frame *fp) static inline unsigned long probe040(int iswrite, unsigned long addr, int wbs) { unsigned long mmusr; + unsigned long old_fc = get_fc(); set_fc(wbs); @@ -191,7 +192,7 @@ static inline unsigned long probe040(int iswrite, unsigned long addr, int wbs) asm volatile (".chip 68040; movec %%mmusr,%0; .chip 68k" : "=r" (mmusr)); - set_fc(USER_DATA); + set_fc(old_fc); return mmusr; } @@ -200,6 +201,7 @@ static inline int do_040writeback1(unsigned short wbs, unsigned long wba, unsigned long wbd) { int res = 0; + unsigned long old_fc = get_fc(); set_fc(wbs); @@ -215,7 +217,7 @@ static inline int do_040writeback1(unsigned short wbs, unsigned long wba, break; } - set_fc(USER_DATA); + set_fc(old_fc); pr_debug("do_040writeback1, res=%d\n", res); diff --git a/arch/m68k/mm/cache.c b/arch/m68k/mm/cache.c index d26eb1a..70fd62b 100644 --- a/arch/m68k/mm/cache.c +++ b/arch/m68k/mm/cache.c @@ -109,14 +109,16 @@ static void __flush_icache_range(unsigned long address, unsigned long endaddr, void flush_icache_user_range(unsigned long address, unsigned long endaddr) { + unsigned long old_fc = get_fc(); __flush_icache_range(address, endaddr, USER_DATA); } void flush_icache_range(unsigned long address, unsigned long endaddr) { + unsigned long old_fc = get_fc(); set_fc(SUPER_DATA); __flush_icache_range(address, endaddr, SUPER_DATA); - set_fc(USER_DATA); + set_fc(old_fc); } EXPORT_SYMBOL(flush_icache_range); -- 2.7.4 --------------3E293333351F33042270B84D--