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SubjectRe: [RFC PATCH] x86 NMI-safe INT3 and Page Fault (v7)
* Jeremy Fitzhardinge (jeremy@goop.org) wrote:
> Mathieu Desnoyers wrote:
>> * Jeremy Fitzhardinge (jeremy@goop.org) wrote:
>>
>>> Mathieu Desnoyers wrote:
>>>
>>>> +/*
>>>> + * Only returns from a trap or exception to a NMI context
>>>> (intra-privilege
>>>> + * level near return) to the same SS and CS segments. Should be used
>>>> + * upon trap or exception return when nested over a NMI context so no
>>>> iret is
>>>> + * issued. It takes care of modifying the eflags, rsp and returning to
>>>> the
>>>> + * previous function.
>>>> + *
>>>> + * The stack, at that point, looks like :
>>>> + *
>>>> + * 0(rsp) RIP
>>>> + * 8(rsp) CS
>>>> + * 16(rsp) EFLAGS
>>>> + * 24(rsp) RSP
>>>> + * 32(rsp) SS
>>>> + *
>>>> + * Upon execution :
>>>> + * Copy EIP to the top of the return stack
>>>> + * Update top of return stack address
>>>> + * Pop eflags into the eflags register
>>>> + * Make the return stack current
>>>> + * Near return (popping the return address from the return stack)
>>>> + */
>>>> +#define INTERRUPT_RETURN_NMI_SAFE pushq %rax; \
>>>> + mov %rsp, %rax; \
>>>> + mov 24+8(%rax), %rsp; \
>>>> + pushq 0+8(%rax); \
>>>> + pushq 16+8(%rax); \
>>>> + movq (%rax), %rax; \
>>>> + popfq; \
>>>> + ret;
>>>>
>>> I got this right first go? I must be getting good at this...
>>>
>>>
>>
>> Yes, it looked good to me at least :)
>>
>>
>>> Anyway, trailing ';', and perhaps use a consistent form for mov (either
>>> movq or mov in all three instances).
>>>
>>>
>>
>> Ok, fixed. Here is the update.
>>
>> The last issue standing would be the paravirt code. Any ideas about how
>> it's best to do it ? It would be good to be able to get the nmi-safe
>> version on bare metal, patched with a standard iret emulation in
>> paravirt code.
>>
>
> #ifdef CONFIG_PARAVIRT
> #define NMI_RETURN paravirt_nmi_return
>
> /* elsewhere */
> .nmi_return = native_iret_nmi_return;
> #else
> #define NMI_RETURN NMI_SAFE_NMI_RETURN
> #endif
>
> ?
>

Then I guess we would have to start dealing with faults caused by popf
if it happens to be run before the code patching is done ?

Mathieu

> J

--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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