On Mon, Aug 11, 2014 at 01:26:45AM +0000, Sha, Ruibin wrote: > Hi Chintan, > Thank you very much for your timely and kindly response and comments. > > Here is more detail about our Scenario: > > We have a big driver on Android product. The driver allocates lots of > DDR pages. When applications mmap a file exported from the driver, > driver would mmap the pages to the application space, usually with > uncachable prot. > On ia32/x86_64 arch, we have to avoid page cache alias issue. When > driver allocates the pages, it would change page original mapping in > page table with uncachable prot. Sometimes, the allocated page was > used by kmap/kunmap. After kunmap, the page is still mapped in KMAP > space. The entries in KMAP page table are not cleaned up until a > kernel thread flushes the freed KMAP pages(usually it is woken up by kunmap). > It means the driver need force to flush the KMAP page table entries before mapping pages to > application space to be used. Otherwise, there is a race to create > cache alias. > > To resolve this issue, we need export function kmap_flush_unused as > the driver is compiled as module. Then, the driver calls > kmap_flush_unused if the allocated pages are in HIGHMEM and being > used by kmap. A: Because it messes up the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail? That said, it sounds like you want set_memory_() to call kmap_flush_unused(). Because this race it not at all specific to your usage, it could happen to any set_memory_() site, right?
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