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Subject: Re: [PATCH 02/16] x86/entry/32: Enter the kernel via trampoline stack
To: Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
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From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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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