On Mon, 2006-06-05 at 15:44 +0100, Russell King wrote: > Hence I find your comment "There are two cases where devices kmap a > user page into kernel space and then proceed to read from or write to > it" to be misleading - at the exact point in time that the device > driver is manipulating the data in that page, it is not a user page. zero copy doesn't quite follow that ownership model. We don't really do anything to block user access to the page while I/O is underway (the only time we actually do this is the nopage stuff) if the user wants do do something stupid like write to a page they've asked us to read data into, the resulting coherency cockup is their lookout, and which data actually ends up in the page undefined. So, both the user and the kernel mappings exist on the page while it's undergoing kmap and modification. However, regardless of whether it's mapped into user space or not, even if it were later going to be mapped at a non-congruent user address, the kernel mappings have to be flushed to make the data written via them visible to the user (and, for a VIPT cache, they have to be flushed before the mapping is torn down otherwise we might not have the PTE to flush them via ...) James - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
