Date: Wed, 14 Sep 2016 15:19:24 +0300 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Andriy Gapon <avg@FreeBSD.org>, stable@FreeBSD.org Subject: Re: X2APIC support Message-ID: <20160914121924.GA2840@zxy.spb.ru> In-Reply-To: <20160914113634.GF38409@kib.kiev.ua> References: <b03e7fa0-b73f-de92-b783-de8be2d66107@FreeBSD.org> <20160913121133.GX34394@zxy.spb.ru> <71a1f864-66de-0010-5024-e8e985f422f4@FreeBSD.org> <20160913124239.GZ34394@zxy.spb.ru> <c6e1a647-344b-a6d7-9f48-65092533ed21@FreeBSD.org> <20160913142118.GA34394@zxy.spb.ru> <37f5cebc-3fa1-9e95-5123-f3d8daa3130a@FreeBSD.org> <20160913152240.GE38409@kib.kiev.ua> <cb35f671-95e7-820f-6a78-ee60612cc1ad@FreeBSD.org> <20160914113634.GF38409@kib.kiev.ua>
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On Wed, Sep 14, 2016 at 02:36:34PM +0300, Konstantin Belousov wrote: > On Tue, Sep 13, 2016 at 06:52:19PM +0300, Andriy Gapon wrote: > > On 13/09/2016 18:22, Konstantin Belousov wrote: > > > Any access > > > to the LAPIC registers page in x2APIC mode faults. > > > > Is this a fact? > > I read the following in the specification: > > > > In x2APIC mode, the memory mapped interface is not available and any > > access to the MMIO interface will behave similar to that of a legacy xAPIC > > in globally disabled state. > > > > But I couldn't find what actually happens for the legacy xAPIC in globally > > disabled state. For AMD processors it is documented that if xAPIC is disabled > > then accessing the APIC memory range works the same as accessing the regular > > memory. That can be different for Intel processors, of course. > > Look at the native_lapic_init(), very beginning of the function. If > x2apic_mode is non-zero, lapic_map is cleared after DMAP page cache > attributes are changed. > > Right now, if BIOS pass control to OS in x2APIC mode, thinks just work > because no LAPIC accesses are done until native_lapic_enable_x2apic() is > called. This just happens, I thought about more organized receipt of the > current LAPIC mode. Issue is that decision for LAPIC mode is performed > by madt enumerator which pref. should not read LAPIC config (too early). > And it is not clear at all, what to do if there is reason to use xAPIC, > as checked by madt_setup_local(), but we are in x2APIC mode already. > > Anyway, returning to the original issue, I do not believe that the > hand-off on that machine occured in the x2APIC mode when X2APIC_OPT_OUT > is specified. Kernel would fault in that case. As I assume, other OS don't fault in this case.
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