Messages in this thread | | | Date | Wed, 02 May 2018 09:07:24 -0600 | From | "Jan Beulich" <> | Subject | Re: [Xen-devel] [PATCH 4/4] xen/PVH: Remove reserved entry in PVH GDT |
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>>> On 02.05.18 at 17:06, <boris.ostrovsky@oracle.com> wrote: > On 05/02/2018 04:26 AM, Jan Beulich wrote: >>>>> On 01.05.18 at 14:34, <boris.ostrovsky@oracle.com> wrote: >>> On 05/01/2018 04:00 AM, Roger Pau Monné wrote: >>>> On Mon, Apr 30, 2018 at 12:23:39PM -0400, Boris Ostrovsky wrote: >>>>> And without it we can't use _BOOT_XX macros any longer so define new ones. >>>> Not being that familiar with Linux internals I'm not sure I see the >>>> benefit of this. Isn't there a risk that some other code is going to >>>> use the __BOOT_XX defines? >>> The startup code we are jumping to loads their own GDT and I don't see >>> any explicit references to segments. >> No explicit references to segments isn't enough: You also need to make >> sure no exceptions at all can occur while loaded selectors and GDT are >> out of sync - in particular NMI might be of concern here (this isn't PV >> after all, where not having a callback registered effectively masks NMI). > > How would keeping __BOOT_XX selectors help with NMI? We don't have > anything set up for NMI handling anyway yet, this is all done in x86 > startup code later.
Oh, you're right - there's no IDT either, so an NMI would yield a triple fault anyway.
Jan
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