Hi Nick, -----Original Message----- From: Nick Piggin [mailto:nickpiggin@xxxxxxxxxxxx] Sent: Friday, April 27, 2007 11:03 PM To: Hugh Dickins Cc: rohitseth@xxxxxxxxxx; Mike Stroyan; Andrew Morton; Luck, Tony; linux-ia64@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx Subject: Re: Fw: [PATCH] ia64: race flushing icache in do_no_page path Hugh Dickins wrote: > On Sat, 28 Apr 2007, Nick Piggin wrote: > >>OIC, you need a virtual address to evict the icache, so you can't >>flush at flush_dcache time? Or does ia64 have an instruction to flush >>the whole icache? (it would be worth testing, to see how much >>performance suffers). > > > I'm puzzled by that remark: the ia64 flush_icache_range always has a > virtual address, it uses the kernel virtual address; it takes no > interest in whether there's a user virtual address. >I _think_ what it is doing is actually flushing dcache lines dirtied >via the kernel virtual address (yes, I think flush_icache > in lazy_mmu_prot_update is actually just flushing the dcache, but >I could be wrong? [*]). It is invalidating any entries (containing same physical address) in both I and D caches. Any dirty lines in D cache are written back to memory before getting invalidated (ofcourse). > There are supposedly no icache lines at that point[**]: For this bug to trigger there has to be a (stale) entry in icache containing the old contents of a page that just got updated by kernel as explicit copying of data (DMAs are coherent on ia64, meaning if a device were to write to memory then architecture guarnatees that both I and D caches are invalidated). > the bug fix at the start of this thread >is due to icache lines becoming present before the flush. For this mail thread, the old contents were not flushed out of icache when the old mapping was removed. And they were still present when the free page got mapped again. Cheers, -rohit - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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