Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751077AbWITHZ2 (ORCPT ); Wed, 20 Sep 2006 03:25:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751252AbWITHZ2 (ORCPT ); Wed, 20 Sep 2006 03:25:28 -0400 Received: from jaguar.mkp.net ([192.139.46.146]:63111 "EHLO jaguar.mkp.net") by vger.kernel.org with ESMTP id S1751077AbWITHZ1 (ORCPT ); Wed, 20 Sep 2006 03:25:27 -0400 To: Linus Torvalds Cc: Linux Kernel Mailing List , bjorn_helgaas@hp.com, Nick Piggin , Andrew Morton , Robin Holt , Dean Nelson , Hugh Dickins Subject: [patch] do_no_pfn() From: Jes Sorensen Date: 20 Sep 2006 03:25:25 -0400 In-Reply-To: Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.4 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5260 Lines: 139 Ahoy Cap'n Since the ship has docked, the cargo doors must be all open and ready to take another load of stuff destined for exotic places. Yet again, I would like to add the do_no_pfn() patch which we discussed earlier. Nothing has changed in it for months and you haven't raised any eyebrows over it since the last discussion where you said it could play within the rules, so maybe this is a good time? Cheers, Jes Implement do_no_pfn() for handling mapping of memory without a struct page backing it. This avoids creating fake page table entries for regions which are not backed by real memory. This feature is used by the MSPEC driver and other users, where it is highly undesirable to have a struct page sitting behind the page (for instance if the page is accessed in cached mode via the struct page in parallel to the the driver accessing it uncached, which can result in data corruption on some architectures, such as ia64). This version uses specific NOPFN_{SIGBUS,OOM} return values, rather than expect all negative pfn values would be an error. It also bugs on cow mappings as this would not work with the VM. Signed-off-by: Jes Sorensen --- include/linux/mm.h | 7 +++++ mm/memory.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++----- 2 files changed, 64 insertions(+), 5 deletions(-) Index: linux-2.6/include/linux/mm.h =================================================================== --- linux-2.6.orig/include/linux/mm.h +++ linux-2.6/include/linux/mm.h @@ -197,6 +197,7 @@ struct vm_operations_struct { void (*open)(struct vm_area_struct * area); void (*close)(struct vm_area_struct * area); struct page * (*nopage)(struct vm_area_struct * area, unsigned long address, int *type); + unsigned long (*nopfn)(struct vm_area_struct * area, unsigned long address); int (*populate)(struct vm_area_struct * area, unsigned long address, unsigned long len, pgprot_t prot, unsigned long pgoff, int nonblock); /* notification that a previously read-only page is about to become @@ -625,6 +626,12 @@ static inline int page_mapped(struct pag #define NOPAGE_OOM ((struct page *) (-1)) /* + * Error return values for the *_nopfn functions + */ +#define NOPFN_SIGBUS ((unsigned long) -1) +#define NOPFN_OOM ((unsigned long) -2) + +/* * Different kinds of faults, as returned by handle_mm_fault(). * Used to decide whether a process gets delivered SIGBUS or * just gets major/minor fault counters bumped up. Index: linux-2.6/mm/memory.c =================================================================== --- linux-2.6.orig/mm/memory.c +++ linux-2.6/mm/memory.c @@ -2211,6 +2211,52 @@ oom: } /* + * do_no_pfn() tries to create a new page mapping for a page without + * a struct_page backing it + * + * As this is called only for pages that do not currently exist, we + * do not need to flush old virtual caches or the TLB. + * + * We enter with non-exclusive mmap_sem (to exclude vma changes, + * but allow concurrent faults), and pte mapped but not yet locked. + * We return with mmap_sem still held, but pte unmapped and unlocked. + * + * It is expected that the ->nopfn handler always returns the same pfn + * for a given virtual mapping. + */ +static int do_no_pfn(struct mm_struct *mm, struct vm_area_struct *vma, + unsigned long address, pte_t *page_table, pmd_t *pmd, + int write_access) +{ + spinlock_t *ptl; + pte_t entry; + unsigned long pfn; + int ret = VM_FAULT_MINOR; + + pte_unmap(page_table); + BUG_ON(!(vma->vm_flags & VM_PFNMAP)); + BUG_ON(is_cow_mapping(vma->vm_flags)); + + pfn = vma->vm_ops->nopfn(vma, address & PAGE_MASK); + if (pfn == NOPFN_OOM) + return VM_FAULT_OOM; + if (pfn == NOPFN_SIGBUS) + return VM_FAULT_SIGBUS; + + page_table = pte_offset_map_lock(mm, pmd, address, &ptl); + + /* Only go through if we didn't race with anybody else... */ + if (pte_none(*page_table)) { + entry = pfn_pte(pfn, vma->vm_page_prot); + if (write_access) + entry = maybe_mkwrite(pte_mkdirty(entry), vma); + set_pte_at(mm, address, page_table, entry); + } + pte_unmap_unlock(page_table, ptl); + return ret; +} + +/* * Fault of a previously existing named mapping. Repopulate the pte * from the encoded file_pte if possible. This enables swappable * nonlinear vmas. @@ -2272,11 +2318,17 @@ static inline int handle_pte_fault(struc old_entry = entry = *pte; if (!pte_present(entry)) { if (pte_none(entry)) { - if (!vma->vm_ops || !vma->vm_ops->nopage) - return do_anonymous_page(mm, vma, address, - pte, pmd, write_access); - return do_no_page(mm, vma, address, - pte, pmd, write_access); + if (vma->vm_ops) { + if (vma->vm_ops->nopage) + return do_no_page(mm, vma, address, + pte, pmd, + write_access); + if (vma->vm_ops->nopfn) + return do_no_pfn(mm, vma, address, pte, + pmd, write_access); + } + return do_anonymous_page(mm, vma, address, + pte, pmd, write_access); } if (pte_file(entry)) return do_file_page(mm, vma, address, - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/