Re: [PATCH v5 28/32] x86/mm, kexec: Allow kexec to be used with SME

Tom Lendacky
2017-05-19T21:38:27Z

On 5/19/2017 4:28 PM, Borislav Petkov wrote:
> On Fri, May 19, 2017 at 04:07:24PM -0500, Tom Lendacky wrote:
>> As long as those never change from static inline everything will be
>> fine. I can change it, but I really like how it explicitly indicates
>
> I know what you want to do. But you're practically defining a helper
> which contains two arbitrary instructions which probably no one else
> will need.
>
> So how about we simplify this function even more. We don't need to pay
> attention to kexec being in progress because we're halting anyway so who
> cares how fast we halt.
>
> Might have to state that in the comment below though, instead of what's
> there now.
>
> And for the exact same moot reason, we don't need to look at SME CPUID
> feature - we can just as well WBINVD unconditionally.
>
> void stop_this_cpu(void *dummy)
> {
> local_irq_disable();
> /*
> * Remove this CPU:
> */
> set_cpu_online(smp_processor_id(), false);
> disable_local_APIC();
> mcheck_cpu_clear(this_cpu_ptr(&cpu_info));
>
> for (;;) {
> /*
> * If we are performing a kexec and the processor supports
> * SME then we need to clear out cache information before
> * halting. With kexec, going from SME inactive to SME active
> * requires clearing cache entries so that addresses without
> * the encryption bit set don't corrupt the same physical
> * address that has the encryption bit set when caches are
> * flushed. Perform a wbinvd followed by a halt to achieve
> * this.
> */
> asm volatile("wbinvd; hlt" ::: "memory");
> }
> }
>
> How's that?

I can live with that!

Thanks,
Tom

>