linux-kernel - Re: [PATCH 20/43] x86/entry: Clean up SYSENTER

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Message-ID: <alpine.DEB.2.20.1711251749120.2316@nanos>
Date:   Sat, 25 Nov 2017 17:50:10 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>
cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [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