From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 548F9B7B8C for ; Fri, 25 Sep 2009 13:03:55 +1000 (EST) Subject: Re: [PATCH] powerpc/8xx: fix regression introduced by cache coherency rewrite From: Benjamin Herrenschmidt To: Rex Feany In-Reply-To: <1253843480.7103.492.camel@pasglop> References: <20090924004552.GA11737@compile2.chatsunix.int.mrv.com> <1253774659.7103.405.camel@pasglop> <20090924233346.GA445@compile2.chatsunix.int.mrv.com> <1253836376.7103.469.camel@pasglop> <20090925013528.GA2584@compile2.chatsunix.int.mrv.com> <1253843480.7103.492.camel@pasglop> Content-Type: text/plain Date: Fri, 25 Sep 2009 13:03:47 +1000 Message-Id: <1253847827.7103.504.camel@pasglop> Mime-Version: 1.0 Cc: "linuxppc-dev@ozlabs.org" List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , > I think there's more finishyness to 8xx than we thought. IE. That > tlbil_va might have more reasons to be there than what the comment > seems to advertize. Can you try to move it even higher up ? IE. > Unconditionally at the beginning of set_pte_filter ? > > Also, if that doesn't help, can you try putting one in > set_access_flags_filter() just below ? Ok, I got a refresher on the whole concept of "unpopulated TLB entries" on 8xx, and that's damn scary. I think what mislead me initially is that the comment around the workaround is simply not properly describing the extent of the problem :-) So I'm not going to make the 8xx TLB miss code sane, that's beyond what I'm prepare to do with it, but I suspect that this should fix it (on top of upstream). Let me know if that's enough or if we also need to put one of these in ptep_set_access_flags(). Please let me know if that works for you. Cheers, Ben. diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c index 5304093..7a8e676 100644 --- a/arch/powerpc/mm/pgtable.c +++ b/arch/powerpc/mm/pgtable.c @@ -170,6 +170,16 @@ struct page * maybe_pte_to_page(pte_t pte) static pte_t set_pte_filter(pte_t pte, unsigned long addr) { +#ifdef CONFIG_8xx + /* 8xx has a weird concept of "unpopulated" entries. When we take + * a TLB miss for a non-valid PTE, we insert such an entry which + * causes a page fault the next time around. This entry must now + * be kicked out or we'll just fault again + */ + /* 8xx doesn't care about PID, size or ind args */ + _tlbil_va(addr, 0, 0, 0); +#endif /* CONFIG_8xx */ + pte = __pte(pte_val(pte) & ~_PAGE_HPTEFLAGS); if (pte_looks_normal(pte) && !(cpu_has_feature(CPU_FTR_COHERENT_ICACHE) || cpu_has_feature(CPU_FTR_NOEXECUTE))) { @@ -177,17 +187,6 @@ static pte_t set_pte_filter(pte_t pte, unsigned long addr) if (!pg) return pte; if (!test_bit(PG_arch_1, &pg->flags)) { -#ifdef CONFIG_8xx - /* On 8xx, cache control instructions (particularly - * "dcbst" from flush_dcache_icache) fault as write - * operation if there is an unpopulated TLB entry - * for the address in question. To workaround that, - * we invalidate the TLB here, thus avoiding dcbst - * misbehaviour. - */ - /* 8xx doesn't care about PID, size or ind args */ - _tlbil_va(addr, 0, 0, 0); -#endif /* CONFIG_8xx */ flush_dcache_icache_page(pg); set_bit(PG_arch_1, &pg->flags); }