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From:   Andy Lutomirski <luto@kernel.org>
Date:   Wed, 16 Jan 2019 16:09:52 -0800
Message-ID: <CALCETrXhDXbi7q6w7EkaT7=9P90kUuivQhz3B0HtoBapFgjkuA@mail.gmail.com>
Subject: Re: [PATCH v3] x86-64/Xen: fix stack switching
To:     Jan Beulich <JBeulich@suse.com>
Cc:     Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andrew Lutomirski <luto@kernel.org>,
        xen-devel <xen-devel@lists.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, Jan 15, 2019 at 8:58 AM Jan Beulich <JBeulich@suse.com> 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 <luto@kernel.org>