site_archiver@lists.apple.com Delivered-To: darwin-kernel@lists.apple.com On Jun 30, 2005, at 4:55 PM, Andrew Gallatin wrote: It seems rock solid for small buffers, but once I get over a few hundred megs, I see some "interesting" corruption. The corruption starts at user address 0x10000000 and continues through the page starting at 0x1006f000. Another "bad spot" appears at 0x20000000 and continues through the page starting at 0x2006f000. Moreover, the contents which should appear at 0x20000000..0x2006ffff appear at 0x10000000..0x1006ffff, while I see stale data at 0x20000000..0x2006ffff. This makes it seem like large copyouts which cross a 256MB boundary may wrap around, and write to exactly 256MB below the desired address. 256MB boundaries are "magic" as they denote the PPC "segment" to be referenced, and segment registers are part of the PPC VM translation mechanism. Simply put, each 256MB-aligned chunk is translated using a different segment register value. (For 32-bit PPCs, the segment ID is the virtual address & 0xf0000000). The copyin/copyout mechanism works in an interesting manner, mapping 512MB chunks of the user memory space into the kernel address range 0xe0000000 - 0xffffffff. So for example, accesses to virtual address 0x1000 would be mapped via the kernel to kernel address 0xe0001000. For what you're seeing to make sense, what must be happening is that since you're wrapping around a 256MB boundary, the segment register that SHOULD be programmed for the next 256MB "chunk" is actually being programmed to point to the original 256MB chunk. Do you see this same failure on 32-bit PPCs, or just on G5s? I know you mentioned your test machine was a G5, but I'm just curious if we can rule out the 32-bit VM code here. William Kucharski kucharsk@mac.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... This email sent to site_archiver@lists.apple.com