On Thu, Dec 21, 2006 at 06:55:47PM +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. > > I'm not sure I understand. flush_anon_page() needs only to flush the > mapping for the given virtual address, no?
Yes, but that virtual /user/ address is meaningless without knowing which process address space it belongs to. > It's always mapped at that address (since it was just accessed through > that). No. Consider ptrace() (invoked by gdb) reading data from another processes address space to obtain structure data or instructions. > Any other mappings > of the anonymous page are irrelevant, they don't need to be flushed. Again, incorrect. Consider if the page you're accessing is a file- backed page, and is mapped into a process using a shared mapping. Because you've written to the file, those shared mappings need to see that write, and the interface for achieving that is flush_dcache_page(). If not, data loss can occur. > > 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. > > I think calling get_user_pages() from a different process' address > space simply doesn't make any sense. That was it's main use - to implement ptrace() to read other processes address spaces. Why do you think it takes a task_struct and mm_struct? -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/