linux-kernel - Re: fuse, get_user_pages, flush_anon_page, aliasing caches and all that again

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Message-ID: <20061221171739.GE3958@flint.arm.linux.org.uk>
Date:	Thu, 21 Dec 2006 17:17:39 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: fuse, get_user_pages, flush_anon_page, aliasing caches and all that again

On Thu, Dec 21, 2006 at 04:53:56PM +0100, Miklos Szeredi wrote:
> Yes, note the flush_dcache_page() call in fuse_copy_finish().  That
> could be replaced by the flush_kernel_dcache_page() (added by James
> Bottomley together with flush_anon_page()) when all relevant
> architectures have defined it.

I should say that flush_anon_page() in its current form is going to be
problematic for ARM.  It is passed:

1. the struct page
2. the virtual address in process memory for the page

It is not passed the mm or vma.  This means that we have no idea whether
the virtual address is in the currently mapped VM space or not.  The
common use of get_area_pages() is to get pages from other address
spaces.

If we use the supplied virtual address to perform cache maintainence of
the userspace mapping, we might end up hitting a completely different
processes address space, which may contain some page sensitive to such
operations, or may not contain any page and thereby could cause a page
fault on some ARM CPUs.

Hence, I first need something like this patch so I can tell if the
page to be flushed is in the current VMs address space or not:

diff --git a/Documentation/cachetlb.txt b/Documentation/cachetlb.txt
index 73e794f..920d0f6 100644
--- a/Documentation/cachetlb.txt
+++ b/Documentation/cachetlb.txt
@@ -373,7 +373,8 @@ maps this page at its virtual address.
 	likely that you will need to flush the instruction cache
 	for copy_to_user_page().
 
-  void flush_anon_page(struct page *page, unsigned long vmaddr)
+  void flush_anon_page(struct vm_area_struct *vma, struct page *page,
+                       unsigned long vmaddr)
   	When the kernel needs to access the contents of an anonymous
 	page, it calls this function (currently only
 	get_user_pages()).  Note: flush_dcache_page() deliberately
diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c
diff --git a/include/asm-arm/cacheflush.h b/include/asm-arm/cacheflush.h
diff --git a/include/asm-parisc/cacheflush.h b/include/asm-parisc/cacheflush.h
index aedb051..a799dd8 100644
--- a/include/asm-parisc/cacheflush.h
+++ b/include/asm-parisc/cacheflush.h
@@ -186,7 +186,7 @@ flush_cache_page(struct vm_area_struct *
 }
 
 static inline void
-flush_anon_page(struct page *page, unsigned long vmaddr)
+flush_anon_page(struct vm_area_struct *vma, struct page *page, unsigned long vmaddr)
 {
 	if (PageAnon(page))
 		flush_user_dcache_page(vmaddr);
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index ca9a602..645d440 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -8,7 +8,7 @@ #include <linux/uaccess.h>
 #include <asm/cacheflush.h>
 
 #ifndef ARCH_HAS_FLUSH_ANON_PAGE
-static inline void flush_anon_page(struct page *page, unsigned long vmaddr)
+static inline void flush_anon_page(struct vm_area_struct *vma, struct page *page, unsigned long vmaddr)
 {
 }
 #endif
diff --git a/mm/memory.c b/mm/memory.c
index c00bac6..13970fe 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1091,7 +1091,7 @@ int get_user_pages(struct task_struct *t
 			if (pages) {
 				pages[i] = page;
 
-				flush_anon_page(page, start);
+				flush_anon_page(vma, page, start);
 				flush_dcache_page(page);
 			}
 			if (vmas)


-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
-
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