From 672ca28e300c17bf8d792a2a7a8631193e580c74 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 23 Jun 2008 11:21:37 -0700 Subject: [PATCH] Fix ZERO_PAGE breakage with vmware Commit 89f5b7da2a6bad2e84670422ab8192382a5aeb9f ("Reinstate ZERO_PAGE optimization in 'get_user_pages()' and fix XIP") broke vmware, as reported by Jeff Chua: "This broke vmware 6.0.4. Jun 22 14:53:03.845: vmx| NOT_IMPLEMENTED /build/mts/release/bora-93057/bora/vmx/main/vmmonPosix.c:774" and the reason seems to be that there's an old bug in how we handle do FOLL_ANON on VM_SHARED areas in get_user_pages(), but since it only triggered if the whole page table was missing, nobody had apparently hit it before. The recent changes to 'follow_page()' made the FOLL_ANON logic trigger not just for whole missing page tables, but for individual pages as well, and exposed this problem. This fixes it by making the test for when FOLL_ANON is used more careful, and also makes the code easier to read and understand by moving the logic to a separate inline function. Reported-and-tested-by: Jeff Chua Signed-off-by: Linus Torvalds --- mm/memory.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 9aefaae..423e0e7 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1045,6 +1045,26 @@ no_page_table: return page; } +/* Can we do the FOLL_ANON optimization? */ +static inline int use_zero_page(struct vm_area_struct *vma) +{ + /* + * We don't want to optimize FOLL_ANON for make_pages_present() + * when it tries to page in a VM_LOCKED region. As to VM_SHARED, + * we want to get the page from the page tables to make sure + * that we serialize and update with any other user of that + * mapping. + */ + if (vma->vm_flags & (VM_LOCKED | VM_SHARED)) + return 0; + /* + * And if we have a fault or a nopfn routine, it's not an + * anonymous region. + */ + return !vma->vm_ops || + (!vma->vm_ops->fault && !vma->vm_ops->nopfn); +} + int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, int len, int write, int force, struct page **pages, struct vm_area_struct **vmas) @@ -1119,8 +1139,7 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, foll_flags = FOLL_TOUCH; if (pages) foll_flags |= FOLL_GET; - if (!write && !(vma->vm_flags & VM_LOCKED) && - (!vma->vm_ops || !vma->vm_ops->fault)) + if (!write && use_zero_page(vma)) foll_flags |= FOLL_ANON; do { -- 2.7.4