From: Ross Zwisler Subject: [PATCH v5 1/5] mm: add vm_insert_mixed_mkwrite() Date: Mon, 24 Jul 2017 11:06:12 -0600 Message-ID: <20170724170616.25810-2-ross.zwisler@linux.intel.com> References: <20170724170616.25810-1-ross.zwisler@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Theodore Ts'o , Matthew Wilcox , "Darrick J. Wong" , Dave Chinner , Jonathan Corbet , Steven Rostedt , linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-xfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Ingo Molnar , Andreas Dilger , Alexander Viro , linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Jan Kara , linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Christoph Hellwig , linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org To: Andrew Morton , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Return-path: In-Reply-To: <20170724170616.25810-1-ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" List-Id: linux-ext4.vger.kernel.org To be able to use the common 4k zero page in DAX we need to have our PTE fault path look more like our PMD fault path where a PTE entry can be marked as dirty and writeable as it is first inserted rather than waiting for a follow-up dax_pfn_mkwrite() => finish_mkwrite_fault() call. Right now we can rely on having a dax_pfn_mkwrite() call because we can distinguish between these two cases in do_wp_page(): case 1: 4k zero page => writable DAX storage case 2: read-only DAX storage => writeable DAX storage This distinction is made by via vm_normal_page(). vm_normal_page() returns false for the common 4k zero page, though, just as it does for DAX ptes. Instead of special casing the DAX + 4k zero page case we will simplify our DAX PTE page fault sequence so that it matches our DAX PMD sequence, and get rid of the dax_pfn_mkwrite() helper. We will instead use dax_iomap_fault() to handle write-protection faults. This means that insert_pfn() needs to follow the lead of insert_pfn_pmd() and allow us to pass in a 'mkwrite' flag. If 'mkwrite' is set insert_pfn() will do the work that was previously done by wp_page_reuse() as part of the dax_pfn_mkwrite() call path. Signed-off-by: Ross Zwisler Reviewed-by: Jan Kara --- include/linux/mm.h | 2 ++ mm/memory.c | 50 +++++++++++++++++++++++++++++++++++++++++++------- 2 files changed, 45 insertions(+), 7 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 46b9ac5..483e84c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2293,6 +2293,8 @@ int vm_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr, unsigned long pfn, pgprot_t pgprot); int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr, pfn_t pfn); +int vm_insert_mixed_mkwrite(struct vm_area_struct *vma, unsigned long addr, + pfn_t pfn); int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len); diff --git a/mm/memory.c b/mm/memory.c index 0e517be..b29dd42 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1646,7 +1646,7 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr, EXPORT_SYMBOL(vm_insert_page); static int insert_pfn(struct vm_area_struct *vma, unsigned long addr, - pfn_t pfn, pgprot_t prot) + pfn_t pfn, pgprot_t prot, bool mkwrite) { struct mm_struct *mm = vma->vm_mm; int retval; @@ -1658,14 +1658,35 @@ static int insert_pfn(struct vm_area_struct *vma, unsigned long addr, if (!pte) goto out; retval = -EBUSY; - if (!pte_none(*pte)) - goto out_unlock; + if (!pte_none(*pte)) { + if (mkwrite) { + /* + * For read faults on private mappings the PFN passed + * in may not match the PFN we have mapped if the + * mapped PFN is a writeable COW page. In the mkwrite + * case we are creating a writable PTE for a shared + * mapping and we expect the PFNs to match. + */ + if (WARN_ON_ONCE(pte_pfn(*pte) != pfn_t_to_pfn(pfn))) + goto out_unlock; + entry = *pte; + goto out_mkwrite; + } else + goto out_unlock; + } /* Ok, finally just insert the thing.. */ if (pfn_t_devmap(pfn)) entry = pte_mkdevmap(pfn_t_pte(pfn, prot)); else entry = pte_mkspecial(pfn_t_pte(pfn, prot)); + +out_mkwrite: + if (mkwrite) { + entry = pte_mkyoung(entry); + entry = maybe_mkwrite(pte_mkdirty(entry), vma); + } + set_pte_at(mm, addr, pte, entry); update_mmu_cache(vma, addr, pte); /* XXX: why not for insert_page? */ @@ -1736,14 +1757,15 @@ int vm_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr, track_pfn_insert(vma, &pgprot, __pfn_to_pfn_t(pfn, PFN_DEV)); - ret = insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot); + ret = insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot, + false); return ret; } EXPORT_SYMBOL(vm_insert_pfn_prot); -int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr, - pfn_t pfn) +static int __vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr, + pfn_t pfn, bool mkwrite) { pgprot_t pgprot = vma->vm_page_prot; @@ -1772,10 +1794,24 @@ int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr, page = pfn_to_page(pfn_t_to_pfn(pfn)); return insert_page(vma, addr, page, pgprot); } - return insert_pfn(vma, addr, pfn, pgprot); + return insert_pfn(vma, addr, pfn, pgprot, mkwrite); +} + +int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr, + pfn_t pfn) +{ + return __vm_insert_mixed(vma, addr, pfn, false); + } EXPORT_SYMBOL(vm_insert_mixed); +int vm_insert_mixed_mkwrite(struct vm_area_struct *vma, unsigned long addr, + pfn_t pfn) +{ + return __vm_insert_mixed(vma, addr, pfn, true); +} +EXPORT_SYMBOL(vm_insert_mixed_mkwrite); + /* * maps a range of physical memory into the requested pages. the old * mappings are removed. any references to nonexistent pages results -- 2.9.4