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Re: [Xen-devel] [PATCH 6/6] x86/boot: Drop INVALID_VCPU
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 7 Jan 2020 18:07:26 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Tue, 07 Jan 2020 18:07:38 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 07/01/2020 16:52, Jan Beulich wrote:
> On 06.01.2020 16:54, Andrew Cooper wrote:
>> Now that NULL will fault at boot, there is no need for a special constant to
>> signify "current not set up yet".
> Mind making this "... no strong need ..."? The benefit of an easily
> recognizable value goes away, but I guess we'll be fine without.
> IOW I'm not meaning to object.
Fine.
>
>> --- a/xen/arch/x86/setup.c
>> +++ b/xen/arch/x86/setup.c
>> @@ -705,7 +705,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>> /* Critical region without IDT or TSS. Any fault is deadly! */
>>
>> set_processor_id(0);
>> - set_current(INVALID_VCPU); /* debug sanity. */
>> + set_current(NULL); /* debug sanity. */
>> idle_vcpu[0] = current;
> Is any of this actually changing any value in memory?
Yes. Observe:
/* Set up stack. */
lea STACK_SIZE + sym_esi(cpu0_stack), %esp
twice in head.S, meaning that the top-of-stack block is junk at this point.
Explicitly setting it to NULL here seems like a safer option than
trusting that noone has actually used the stack yet.
~Andrew
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