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SubjectRe: [PATCH 20/43] x86/entry: Clean up SYSENTER_stack code
On Sat, 25 Nov 2017, Borislav Petkov wrote:
> > -
> > + wrmsr(MSR_IA32_SYSENTER_ESP, (unsigned long)(cpu_SYSENTER_stack(cpu) + 1), 0);
> > wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long)entry_SYSENTER_32, 0);
>
> Right, so we have now two TSS thingies, AFAICT:
>
> tss = &per_cpu(cpu_tss, cpu);
>
> which is cpu_tss and then indirectly, we have also:
>
> &get_cpu_entry_area((cpu))->tss
>
> And those are two different things in my guest here:
>
> [ 0.044002] tss: 0xf5747000
> [ 0.044706] entry area tss: 0xffef1000
>
> What is the logic here? We carry two TSSs per CPU - one which is RO
> for the entry area and the other is the actual cpu_tss thing? Or am I
> misreading it?

entry area tss is a alias mapping of cpu_tss

+ set_percpu_fixmap_pages(get_cpu_entry_area_index(cpu, tss),
+ &per_cpu(cpu_tss, cpu),
+ sizeof(struct tss_struct) / PAGE_SIZE,
+ PAGE_KERNEL);

Thanks,

tglx

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