Re: Bug: Xen panics with #UD in acpi_processor_idle()

[Keir Fraser <keir@xen.org>]

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On 22/11/2010 13:02, "Rafal Wojtczuk" <rafal@invisiblethingslab.com> wrote:

> Hello,
> 
> There seems to be an issue with handling of
> MSR_IA32_MISC_ENABLE_MONITOR_ENABLE bit in MSR_IA32_MISC_ENABLE. The effect
> is that Xen panics because of #UD after trying to execute "monitor"
> instruction. Most likely Xen does not bother to set this bit, leaving
> it to BIOS. If I understand correctly, it is mere reliability issue, not
> triggerable from any domain.

The issue appears to be be that we do not check for MWAIT support in CPUID,
same as native Linux would do (the flag in MISC_ENABLE MSR also affects
CPUID appropriately). Can you please try the attached patch? If it works I
will apply it to all our trees.

 Thanks,
 Keir

> The problem can be reproduced with Xen-4.0.1 or tip of xen-4.0-testing.hg,
> dom0 being 2.6.32.23-170.xendom0.fc12.x86_64 taken from
> http://fedorapeople.org/~myoung/dom0. Processor is i5-650 on Intel Q57.
> Panic happens just after starting dom0.
> I have verified (by adding rdmsr(MSR_IA32_MISC_ENABLE) in the panic code)
> that indeed MSR_IA32_MISC_ENABLE_MONITOR_ENABLE is not set (it is 810088).
> The same value is present in the msr when in init_done() function.
> If I hardcode setting this bit just before __monitor(), all is fine. So it
> looks like my crappy BIOS has not set this bit, and Xen has not either, yet
> it tried to use monitor/mwait ?
> 
> Somehow offtopic: what is the purpose of cheating about
> MSR_IA32_MISC_ENABLE_MONITOR_ENABLE state to dom0 in rdmsr emulation ?
> xen-4.0-testing.hg/xen/arch/x86/traps.c:2364
>         case MSR_IA32_MISC_ENABLE:
>             if ( rdmsr_safe(regs->ecx, regs->eax, regs->edx) )
>                 goto fail;
>             regs->eax &= ~(MSR_IA32_MISC_ENABLE_PERF_AVAIL |
>                            MSR_IA32_MISC_ENABLE_MONITOR_ENABLE);
>             regs->eax |= MSR_IA32_MISC_ENABLE_BTS_UNAVAIL |
>                          MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL |
>                          MSR_IA32_MISC_ENABLE_XTPR_DISABLE;
>             break;
> 
> Regards,
> Rafal Wojtczuk
> 
> (XEN) ----[ Xen-4.0.2-rc1-pre  x86_64  debug=n  Not tainted ]----
> (XEN) CPU:    0
> (XEN) RIP:    e008:[<ffff82c48018db7f>] acpi_processor_idle+0x3cf/0x810
> (XEN) RFLAGS: 0000000000010086   CONTEXT: hypervisor
> (XEN) rax: ffff8300cacfc000   rbx: ffff830121634840   rcx: 0000000000000000
> (XEN) rdx: 0000000000000000   rsi: 0000000000000020   rdi: 0000000000000000
> (XEN) rbp: ffff830121634900   rsp: ffff82c480367e80   r8:  000000020bc8ef41
> (XEN) r9:  0000000000000004   r10: ffff82c480397120   r11: 0000000000000001
> (XEN) r12: 00000000000000c0   r13: 0000000000f977e3   r14: ffff8300cacfc000
> (XEN) r15: 0000000000000002   cr0: 000000008005003b   cr4: 00000000000026f0
> (XEN) cr3: 0000000119001000   cr2: ffff880000736860
> (XEN) ds: 0000   es: 0000   fs: 0000   gs: 0000   ss: e010   cs: e008
> (XEN) Xen stack trace from rsp=ffff82c480367e80:
> (XEN)    ffffffffffffffff ffff82c48025f100 ffff82c48011f537 ffff8300cacfc000
> (XEN)    ffffffffffffffff ffffffff817db6b0 0000000000000000 0000000000000000
> (XEN)    000000008037a980 000003c7000003c7 ffff82c48037e980 ffff82c480367f28
> (XEN)    ffff82c48025fb00 ffff82c480367f28 ffff82c480367e18 ffff8300cacfc000
> (XEN)    0000000000000002 ffff82c48014f02e ffff8300cacfc000 ffff8300cb4f8000
> (XEN)    00000000ffffffff 0000000000000000 ffffffffffffffff 0000000000000000
> (XEN)    ffffffff817db6b0 ffffffff81683f10 ffffffff81682000 0000000000000246
> (XEN)    0000000000015740 ffff8800077e6160 0000000000000000 0000000000000000
> (XEN)    ffffffff810093aa 0000000000000246 0000000000000000 0000000000000001
> (XEN)    0000010000000000 ffffffff810093aa 000000000000e033 0000000000000246
> (XEN)    ffffffff81683ef8 000000000000e02b 0000000000000000 0000000000000000
> (XEN)    0000000000000000 0000000000000000 0000000000000000 ffff8300cacfc000
> (XEN) Xen call trace:
> (XEN)    [<ffff82c48018db7f>] acpi_processor_idle+0x3cf/0x810
> (XEN)    [<ffff82c48011f537>] timer_softirq_action+0x227/0x370
> (XEN)    [<ffff82c48014f02e>] idle_loop+0x2e/0x90
> (XEN)    
> (XEN) 
> (XEN) ****************************************
> (XEN) Panic on CPU 0:
> (XEN) FATAL TRAP: vector = 6 (invalid opcode)
> (XEN) ****************************************
> (XEN) 
> (XEN) Reboot in five seconds...
> 
> [root@f13q45 xen]# gdb xen-syms
> Reading symbols from /root/xen/xen-4.0-testing.hg/xen/xen-syms...done.
> (gdb) x/2i 0xffff82c48018db7f
>    0xffff82c48018db7f <acpi_processor_idle+975>:        monitor %rax,%rcx,%rdx
>    0xffff82c48018db82 <acpi_processor_idle+978>:        mfence
>  
> 
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diff -r e9156d9d996b xen/arch/x86/acpi/cpu_idle.c
--- a/xen/arch/x86/acpi/cpu_idle.c	Tue Nov 16 11:54:48 2010 +0000
+++ b/xen/arch/x86/acpi/cpu_idle.c	Mon Nov 22 15:12:15 2010 +0000
@@ -717,7 +717,8 @@
     {
     case ACPI_ADR_SPACE_FIXED_HARDWARE:
         if ( xen_cx->reg.bit_width == VENDOR_INTEL &&
-             xen_cx->reg.bit_offset == NATIVE_CSTATE_BEYOND_HALT )
+             xen_cx->reg.bit_offset == NATIVE_CSTATE_BEYOND_HALT &&
+             boot_cpu_has(X86_FEATURE_MWAIT) )
             cx->entry_method = ACPI_CSTATE_EM_FFH;
         else
             cx->entry_method = ACPI_CSTATE_EM_HALT;

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