On 2014/1/22 21:27, Russell King - ARM Linux wrote: > On Wed, Jan 22, 2014 at 07:25:15PM +0800, Wang Nan wrote: >> ARM's kdump is actually corrupted (at least for omap4460), mainly because of >> cache problem: flush_icache_range can't reliably ensure the copied data >> correctly goes into RAM. > > Quite right too. You're mistake here is thinking that flush_icache_range() > should push it to RAM. That's incorrect. > > flush_icache_range() is there to deal with such things as loadable modules > and self modifying code, where the MMU is not being turned off. Hence, it > only flushes to the point of coherency between the I and D caches, and > any further levels of cache between that point and memory are not touched. > Why should it touch any more levels - it's not the function's purpose. > >> After mmu turned off and jump to the trampoline, kexec always failed due >> to random undef instructions. > > We already have code in the kernel which deals with shutting the MMU off. > An instance of how this can be done is illustrated in the soft_restart() > code path, and kexec already uses this. > > One of the first things soft_restart() does is turn off the outer cache - > which OMAP4 does have, but this can only be done if there is a single CPU > running. If there's multiple CPUs running, then the outer cache can't be > disabled, and that's the most likely cause of the problem you're seeing. > You are right, commit b25f3e1c (OMAP4/highbank: Flush L2 cache before disabling) solves my problem, it flushes outer cache before disabling. I have tested it in UP and SMP situations and it works (actually, omap4 has not ready to support kexec in SMP case, I insert an empty cpu_kill() to make it work), so the first 2 patches are unneeded. What about the 3rd one (ARM: allow kernel to be loaded in middle of phymem)?
