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Date:   Wed, 16 Jan 2019 16:09:52 -0800
From:   Andy Lutomirski <>
To:     Jan Beulich <>
Cc:     Ingo Molnar <>, Thomas Gleixner <>,
        "H. Peter Anvin" <>,
        Andrew Lutomirski <>,
        xen-devel <>,
        Boris Ostrovsky <>,
        Juergen Gross <>,
        LKML <>
Subject: Re: [PATCH v3] x86-64/Xen: fix stack switching

On Tue, Jan 15, 2019 at 8:58 AM Jan Beulich <> wrote:
> While in the native case entry into the kernel happens on the trampoline
> stack, PV Xen kernels get entered with the current thread stack right
> away. Hence source and destination stacks are identical in that case,
> and special care is needed.
> Other than in sync_regs() the copying done on the INT80 path isn't
> NMI / #MC safe, as either of these events occurring in the middle of the
> stack copying would clobber data on the (source) stack.
> I'm not altering the similar code in interrupt_entry() and nmi(), as
> those code paths are unreachable afaict when running PV Xen guests.

Acked-by: Andy Lutomirski <>

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