linux-kernel - Re: [PATCH 02/16] x86/entry/32: Enter the kernel via trampoline stack

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Date:   Wed, 17 Jan 2018 10:02:38 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>, aliguori@...zon.com,
        daniel.gruss@...k.tugraz.at, hughd@...gle.com, keescook@...gle.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, jroedel@...e.de
Subject: Re: [PATCH 02/16] x86/entry/32: Enter the kernel via trampoline stack

Hi Boris,

thanks for testing this :)

On Tue, Jan 16, 2018 at 09:47:06PM -0500, Boris Ostrovsky wrote:
> On 01/16/2018 11:36 AM, Joerg Roedel wrote:
> >+.macro SWITCH_TO_KERNEL_STACK nr_regs=0 check_user=0
> 
> 
> This (and next patch's SWITCH_TO_ENTRY_STACK) need X86_FEATURE_PTI check.
> 
> With those macros fixed I was able to boot 32-bit Xen PV guest.

Hmm, on bare metal the stack switch happens regardless of the
X86_FEATURE_PTI feature being set, because we always program tss.sp0
with the systenter stack. How is the kernel entry stack setup on xen-pv?
I think something is missing there instead.

Regards,

	Joerg