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SubjectRe: [PATCH] xenpv: don't BUG when failing to setup NMI callback
On 06/13/2014 08:45 AM, Konrad Rzeszutek Wilk wrote:
> On Fri, Jun 13, 2014 at 01:26:28PM +0200, Vitaly Kuznetsov wrote:
>> some old Xen hypervisors (prior to 3.2) forbid DomUs to register
>> NMI callbacks. E.g. we have the following code in xen-3.1:
>>
>> if ( (d->domain_id != 0) || (v->vcpu_id != 0) )
>> return -EINVAL;
>>
>> Commit 6efa20e49b9cb1db1ab66870cc37323474a75a13 introduced kernel
>> crash in case PV guest fails to register NMI callback. All x86_64
>> PV guests will fail to boot on top of such hypervisors (RHEL5
>> example):
>>
>> (XEN) traps.c:405:d7 Unhandled invalid opcode fault/trap [#6] in domain 7 on VCPU 0 [ec=0000]
>> (XEN) domain_crash_sync called from entry.S
>> (XEN) Domain 7 (vcpu#0) crashed on cpu#3:
>> (XEN) ----[ Xen-3.1.2-389.el5 x86_64 debug=n Not tainted ]----
>> (XEN) CPU: 3
>> (XEN) RIP: e033:[<ffffffff81004d96>]
>> (XEN) RFLAGS: 0000000000000282 CONTEXT: guest
>> (XEN) rax: ffffffffffffffea rbx: 0000000000000000 rcx: 0000000000000002
>> (XEN) rdx: 0000000000000001 rsi: ffffffff81b0fe28 rdi: 0000000000000000
>> (XEN) rbp: ffffffff81b0fe40 rsp: ffffffff81b0fde8 r8: 0000000000000000
>> (XEN) r9: ffffffff81b0fdd0 r10: 0000000000007ff0 r11: 00000000ffffffff
>> (XEN) r12: ffffffff81d65900 r13: 0000000000000000 r14: 0000000000000000
>> (XEN) r15: 0000000000000000 cr0: 0000000080050033 cr4: 00000000000026b0
>> (XEN) cr3: 000000013a263000 cr2: 0000000000000000
>> (XEN) ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: e02b cs: e033
>> ...
>>
>> However it is possible to proceed without NMI callback registered.
>> Change BUG() with warning in case of -EINVAL.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Oh, we had a similar patch - somebody reported it earlier - and we
> just checked the version of Xen:
>
> http://lists.xenproject.org/archives/html/xen-devel/2014-05/msg01474.html
>
> But I can't remember why I didn't post it.
>
> However I do like your path of checking the 'ret'.


Should we be checking both ret and version? NMI callback registration
can return -EINVAL for other reasons (non-canonical address, for example).

-boris


>
> Vitaly, could expand your patch to also do a check in cvt_gate_to_trap
> so that it won't enable the NMI handler and then lets pick your
> patch?
>
>> ---
>> arch/x86/xen/setup.c | 11 ++++++++++-
>> 1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
>> index 821a11a..5b8b180 100644
>> --- a/arch/x86/xen/setup.c
>> +++ b/arch/x86/xen/setup.c
>> @@ -593,8 +593,17 @@ void xen_enable_syscall(void)
>> void xen_enable_nmi(void)
>> {
>> #ifdef CONFIG_X86_64
>> - if (register_callback(CALLBACKTYPE_nmi, (char *)nmi))
>> + int ret;
>> +
>> + ret = register_callback(CALLBACKTYPE_nmi, (char *)nmi);
>> + if (ret == -EINVAL) {
>> + /* Hypervisor probably forbids us to register NMI callback,
>> + that is expected when running on top of Xen-3.1 and older */
>> + pr_warn("xen: failed to register NMI callback\n");
>> + } else if (ret != 0) {
>> + /* Other hypervisor failure */
>> BUG();
>> + }
>> #endif
>> }
>> void __init xen_pvmmu_arch_setup(void)
>> --
>> 1.9.3
>>



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