From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by kanga.kvack.org (Postfix) with ESMTP id BB1508E0001 for ; Mon, 10 Sep 2018 10:46:52 -0400 (EDT) Received: by mail-wr1-f71.google.com with SMTP id 40-v6so18974315wrb.23 for ; Mon, 10 Sep 2018 07:46:52 -0700 (PDT) Received: from pegase1.c-s.fr (pegase1.c-s.fr. [93.17.236.30]) by mx.google.com with ESMTPS id z74-v6si131088wmz.160.2018.09.10.07.46.47 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Sep 2018 07:46:47 -0700 (PDT) From: Christophe Leroy Subject: How to handle PTE tables with non contiguous entries ? Message-ID: Date: Mon, 10 Sep 2018 14:34:37 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: akpm@linux-foundation.org, linux-mm@kvack.org, aneesh.kumar@linux.vnet.ibm.com, Nicholas Piggin , Michael Ellerman , linuxppc-dev@lists.ozlabs.org Cc: LKML Hi, I'm having a hard time figuring out the best way to handle the following situation: On the powerpc8xx, handling 16k size pages requires to have page tables with 4 identical entries. Initially I was thinking about handling this by simply modifying pte_index() which changing pte_t type in order to have one entry every 16 bytes, then replicate the PTE value at *ptep, *ptep+1,*ptep+2 and *ptep+3 both in set_pte_at() and pte_update(). However, this doesn't work because many many places in the mm core part of the kernel use loops on ptep with single ptep++ increment. Therefore did it with the following hack: /* PTE level */ +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES) +typedef struct { pte_basic_t pte, pte1, pte2, pte3; } pte_t; +#else typedef struct { pte_basic_t pte; } pte_t; +#endif @@ -181,7 +192,13 @@ static inline unsigned long pte_update(pte_t *p, : "cc" ); #else /* PTE_ATOMIC_UPDATES */ unsigned long old = pte_val(*p); - *p = __pte((old & ~clr) | set); + unsigned long new = (old & ~clr) | set; + +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES) + p->pte = p->pte1 = p->pte2 = p->pte3 = new; +#else + *p = __pte(new); +#endif #endif /* !PTE_ATOMIC_UPDATES */ #ifdef CONFIG_44x @@ -161,7 +161,11 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr, /* Anything else just stores the PTE normally. That covers all 64-bit * cases, and 32-bit non-hash with 32-bit PTEs. */ +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES) + ptep->pte = ptep->pte1 = ptep->pte2 = ptep->pte3 = pte_val(pte); +#else *ptep = pte; +#endif But I'm not too happy with it as it means pte_t is not a single type anymore so passing it from one function to the other is quite heavy. Would someone have an idea of an elegent way to handle that ? Thanks Christophe