On 10/12/2017 03:27 PM, Andrew Cooper wrote:
> On 12/10/17 20:11, Boris Ostrovsky wrote:
>> On 10/06/2017 10:32 AM, Josh Poimboeuf wrote:
>>> On Thu, Oct 05, 2017 at 04:35:03PM -0400, Boris Ostrovsky wrote:
>>>>> #ifdef CONFIG_PARAVIRT
>>>>> +/*
>>>>> + * Paravirt alternatives are applied much earlier than normal alternatives.
>>>>> + * They are only applied when running on a hypervisor. They replace some
>>>>> + * native instructions with calls to pv ops.
>>>>> + */
>>>>> +void __init apply_pv_alternatives(void)
>>>>> +{
>>>>> + setup_force_cpu_cap(X86_FEATURE_PV_OPS);
>>>> Not for Xen HVM guests.
>>> From what I can tell, HVM guests still use pv_time_ops and
>>> pv_mmu_ops.exit_mmap, right?
>>>
>>>>> + apply_alternatives(__pv_alt_instructions, __pv_alt_instructions_end);
>>>>> +}
>>>> This is a problem (at least for Xen PV guests):
>>>> apply_alternatives()->text_poke_early()->local_irq_save()->...'cli'->death.
>>> Ah, right.
>>>
>>>> It might be possible not to turn off/on the interrupts in this
>>>> particular case since the guest probably won't be able to handle an
>>>> interrupt at this point anyway.
>>> Yeah, that should work. For Xen and for the other hypervisors, this is
>>> called well before irq init, so interrupts can't be handled yet anyway.
>> There is also another problem:
>>
>> [ 1.312425] general protection fault: 0000 [#1] SMP
>> [ 1.312901] Modules linked in:
>> [ 1.313389] CPU: 0 PID: 1 Comm: init Not tainted 4.14.0-rc4+ #6
>> [ 1.313878] task: ffff88003e2c0000 task.stack: ffffc9000038c000
>> [ 1.314360] RIP: 10000e030:entry_SYSCALL_64_fastpath+0x1/0xa5
>> [ 1.314854] RSP: e02b:ffffc9000038ff50 EFLAGS: 00010046
>> [ 1.315336] RAX: 000000000000000c RBX: 000055f550168040 RCX:
>> 00007fcfc959f59a
>> [ 1.315827] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
>> 0000000000000000
>> [ 1.316315] RBP: 000000000000000a R08: 000000000000037f R09:
>> 0000000000000064
>> [ 1.316805] R10: 000000001f89cbf5 R11: ffff88003e2c0000 R12:
>> 00007fcfc958ad60
>> [ 1.317300] R13: 0000000000000000 R14: 000055f550185954 R15:
>> 0000000000001000
>> [ 1.317801] FS: 0000000000000000(0000) GS:ffff88003f800000(0000)
>> knlGS:0000000000000000
>> [ 1.318267] CS: e033 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 1.318750] CR2: 00007fcfc97ab218 CR3: 000000003c88e000 CR4:
>> 0000000000042660
>> [ 1.319235] Call Trace:
>> [ 1.319700] Code: 51 50 57 56 52 51 6a da 41 50 41 51 41 52 41 53 48
>> 83 ec 30 65 4c 8b 1c 25 c0 d2 00 00 41 f7 03 df 39 08 90 0f 85 a5 00 00
>> 00 50 <ff> 15 9c 95 d0 ff 58 48 3d 4c 01 00 00 77 0f 4c 89 d1 ff 14 c5
>> [ 1.321161] RIP: entry_SYSCALL_64_fastpath+0x1/0xa5 RSP: ffffc9000038ff50
>> [ 1.344255] ---[ end trace d7cb8cd6cd7c294c ]---
>> [ 1.345009] Kernel panic - not syncing: Attempted to kill init!
>> exitcode=0x0000000b
>>
>>
>> All code
>> ========
>> 0: 51 push %rcx
>> 1: 50 push %rax
>> 2: 57 push %rdi
>> 3: 56 push %rsi
>> 4: 52 push %rdx
>> 5: 51 push %rcx
>> 6: 6a da pushq $0xffffffffffffffda
>> 8: 41 50 push %r8
>> a: 41 51 push %r9
>> c: 41 52 push %r10
>> e: 41 53 push %r11
>> 10: 48 83 ec 30 sub $0x30,%rsp
>> 14: 65 4c 8b 1c 25 c0 d2 mov %gs:0xd2c0,%r11
>> 1b: 00 00
>> 1d: 41 f7 03 df 39 08 90 testl $0x900839df,(%r11)
>> 24: 0f 85 a5 00 00 00 jne 0xcf
>> 2a: 50 push %rax
>> 2b:* ff 15 9c 95 d0 ff callq *-0x2f6a64(%rip) #
>> 0xffffffffffd095cd <-- trapping instruction
>> 31: 58 pop %rax
>> 32: 48 3d 4c 01 00 00 cmp $0x14c,%rax
>> 38: 77 0f ja 0x49
>> 3a: 4c 89 d1 mov %r10,%rcx
>> 3d: ff .byte 0xff
>> 3e: 14 c5 adc $0xc5,%al
>>
>>
>> so the original 'cli' was replaced with the pv call but to me the offset
>> looks a bit off, no? Shouldn't it always be positive?
> callq takes a 32bit signed displacement, so jumping back by up to 2G is
> perfectly legitimate.
Yes, but
ostr@workbase> nm vmlinux | grep entry_SYSCALL_64_fastpath
ffffffff817365dd t entry_SYSCALL_64_fastpath
ostr@workbase> nm vmlinux | grep " pv_irq_ops"
ffffffff81c2dbc0 D pv_irq_ops
ostr@workbase>
so pv_irq_ops.irq_disable is about 5MB ahead of where we are now. (I
didn't mean that x86 instruction set doesn't allow negative
displacement, I was trying to say that pv_irq_ops always live further down)
>
> The #GP[0] however means that whatever 8 byte value was found at
> -0x2f6a64(%rip) was a non-canonical address.
>
> One option is that the pvops structure hasn't been initialised properly,
It was, I did check that. And just to make sure I re-initialized it
before alt instructions were rewritten.
> but an alternative is that the relocation wasn't processed correctly,
> and the code is trying to reference something which isn't a function
> pointer.
Let me see if I can poke at what's there.
-boris
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