Fix ZERO_PAGE breakage with vmware (672ca28e) · Commits · 戴 / test

Commit ("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 <jeff.chua.linux@gmail.com> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/memory.c

+21 −2

Original line number	Diff line number	Diff line
		@@ -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 {

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