On Jan 6, 2015 7:34 AM, "Borislav Petkov" <bp@xxxxxxxxx> wrote: > > On Mon, Jan 05, 2015 at 12:31:15PM -0800, Andy Lutomirski wrote: > > Do you have context tracking on? > > Yap, it is enabled for whatever reason: > CONFIG_CONTEXT_TRACKING=y > CONFIG_CONTEXT_TRACKING_FORCE=y > CONFIG_HAVE_CONTEXT_TRACKING=y I'll boot a kernel like this on bare metal and see what shakes loose. > > > I assume that's in the historical tree? > > Yeah. > > > > [ 180.059170] ata1.00: exception Emask 0x0 SAct 0x7fffffff SErr 0x0 action 0x6 frozen > > > [ 180.066873] ata1.00: failed command: WRITE FPDMA QUEUED > > > [ 180.072158] ata1.00: cmd 61/08:00:a8:ac:d9/00:00:23:00:00/40 tag 0 ncq 4096 out > > > [ 180.072158] res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout) > > > > That's really weird. The only thing I can think of is that somehow we > > returned to user mode without enabling interrupts. > > Right, considering FIXUP_TOP_OF_STACK is used in a bunch of cases in > entry_64.S, no wonder it corrupts something. > > > This leads me to wonder: why do we save eflags in the R11 pt_regs > > slot? > > That: "If executed in 64-bit mode, SYSRET loads the lower-32 RFLAGS bits > from R11[31:0] and clears the upper 32 RFLAGS bits." Sure, but the code would be simpler if we shoved that value in the EFLAGS slot. > > > This seems entirely backwards, not to mention that it accounts for two > > instructions in each of FIXUP_TOP_OF_STACK and RESTORE_TOP_OF_STACK > > for no apparently reason whatsoever. > > > Can you send the full output from syscall_exit_regs_64 from here: > > > > https://gitorious.org/linux-test-utils/linux-clock-tests/source/34884122b6ebe81d9b96e3e5128b6d6d95082c6e: > > > > with the patch applied (assuming it even gets that far for you)? I > > see results like: > > > > [NOTE] syscall ffff: orig RCX = 1 ss = 2b orig_ss = 6b flags = > > 217 orig_flags = 217 > > > > which seems fine. > > ./syscall_exit_regs_64 > [OK] int80 ffff: AX = ffffffffffffffda > [OK] int80 40000000: AX = ffffffffffffffda > [OK] syscall ffff: RCX = 400962 RIP = 400962 > [OK] syscall ffff: AX = ffffffffffffffda > [NOTE] syscall ffff: orig RCX = 1 ss = 2b orig_ss = 6b flags = 217 orig_flags = 217 > [OK] syscall 40000000: RCX = 400962 RIP = 400962 > [FAIL] syscall 40000000: AX = fffffffffffffff7 > [NOTE] syscall 40000000: orig RCX = 1 ss = 2b orig_ss = 6b flags = 217 orig_flags = 217 > [OK] syscall(ffff): ret = -1, errno = 38 > > > Are you seeing this with the whole series applied or with only this patch? > > I applied this patch only and started seeing those. Then I booted in the > previous kernel and tried to repro but it didn't trigger. > > I'll try hammering on the kernel *without* your patch to see whether I > can trigger it somehow... Hmm. I added and pushed a test for fork, but that didn't turn anything up. And I don't see any bugs in the code. I booted 3.18 plus this patch with context tracking forced on on my laptop, and something seems to have gone wrong. --Andy > > -- > Regards/Gruss, > Boris. > > Sent from a fat crate under my desk. Formatting is fine. > -- -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
