Re: [Xen-devel] [PATCH v2] x86/boot: Make alternative patching NMI-safe

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/02/2018 19:23, Konrad Rzeszutek Wilk wrote:
> On Mon, Feb 05, 2018 at 07:10:33PM +0000, Andrew Cooper wrote:
>> -    apply_alternatives(__alt_instructions, __alt_instructions_end);
>> +    /* Send ourselves an NMI to trigger the callback. */
>> +    self_nmi();
>> +
>> +    /*
>> +     * Sending ourself an NMI isn't architecturally guaranteed to result in
>> +     * the synchronous delivery (although in practice, it appears to be).
>> +     * Poll alt_done for up to 1 second.
>> +     */
>> +    for ( i = 0; !ACCESS_ONCE(alt_done) && i < 1000; ++i )
> Perhaps an #define for this?

I don't really see the point.  I'm fairly sure that no 64bit CPU will
enter this loop, but the APIC spec doesn't guarantee that delivery is
synchronous.

~Andrew

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