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

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Date:   Tue, 16 Jan 2018 21:47:06 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     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



On 01/16/2018 11:36 AM, Joerg Roedel wrote:

>   
>   /*
> + * Switch from the entry-trampline stack to the kernel stack of the
> + * running task.
> + *
> + * nr_regs is the number of dwords to push from the entry stack to the
> + * task stack. If it is > 0 it expects an irq frame at the bottom of the
> + * stack.
> + *
> + * check_user != 0 it will add a check to only switch stacks if the
> + * kernel entry was from user-space.
> + */
> +.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.

-boris