Date: Sun, 4 Sep 2016 19:29:27 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Andriy Gapon <avg@FreeBSD.org> Cc: Slawa Olhovchenkov <slw@zxy.spb.ru>, stable@FreeBSD.org Subject: Re: X2APIC support Message-ID: <20160904162926.GF83214@kib.kiev.ua> In-Reply-To: <f727b18d-6061-fbaf-6afc-1ae66f8cce16@FreeBSD.org> References: <20151212130615.GE70867@zxy.spb.ru> <20151212133513.GL82577@kib.kiev.ua> <20160901112724.GX88122@zxy.spb.ru> <20160901114500.GJ83214@kib.kiev.ua> <20160901121300.GZ88122@zxy.spb.ru> <4ba05c00-f737-f562-553d-a7fa59145768@FreeBSD.org> <20160904151415.GE83214@kib.kiev.ua> <f727b18d-6061-fbaf-6afc-1ae66f8cce16@FreeBSD.org>
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On Sun, Sep 04, 2016 at 06:49:43PM +0300, Andriy Gapon wrote: > On 04/09/2016 18:14, Konstantin Belousov wrote: > > On Sun, Sep 04, 2016 at 11:19:16AM +0300, Andriy Gapon wrote: > >> Kostik, I see one strange thing which is common to both successful and > >> unsuccessful configurations. All "SMP: Added CPU..." lines have "AP" in them. > >> It seems like the platform does not tell explicitly tell which CPU is the BSP, > >> see cpu_add() function. This can break quite a few assumption. And I am not > >> even sure how the successful scenario works. > >> Ah... I see that there is a backup code in cpu_mp_start() where boot_cpu_id is > >> set based on the current CPU's Local APIC ID. I suspect then that this > >> information is incorrect in the failing case. > >> > > Well, there is no easy way to read the LAPIC Id of BSP before LAPICs > > are initialized. BIOS might reprogram LAPIC Ids, so reading from > > CPUID[1].EBX[31:24] might return incorrect data. Even more incorrect > > it might be in the x2APIC state, since 8 bits are not enough for 32bit > > x2APIC Id. > > Hmm, I am not sure how what you are saying here is relevant to the problem. > I believe that cpu_mp_start() is executed (on the BSP) after the BSP's LAPIC is > initialized. So, the code should just work. The order is madt_probe()->madt_probe_cpus()->madt_setup_local(). madt_probe() and madt_probe_cpus() are called from apic_init9) at SI_SUB_TUNABLEs, and madt_probe_cpus()->madt_add_cpu()->lapic_create()-> cpu_add() is how the SMP: ... lines are printed. The madt_setup_local() code is called from apic_setup_local() at SI_SUB_CPU, this is where APIC window is mapped or x2APIC mode is enabled by the call to native_lapic_init(). You cannot get BSP LAPIC Id earlier than native_lapic_init() was executed. mp_start()->cpu_mp_start() is called right after the madt_setup_local(). > > My theory was that the BSP's LAPIC ID was incorrectly programmed by BIOS (firmware). This is possible, of course. But it would not affect "SMP: Added CPU ..." lines.
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