Messages in this thread | | | Date | Thu, 15 Mar 2012 23:58:09 +0100 | From | Steffen Persvold <> | Subject | Re: [PATCH] Use x2apic_supported() in the default_apic_id_valid() function. |
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On 3/15/12 23:34 , Steffen Persvold wrote: > On 3/15/12 22:21 , Suresh Siddha wrote: >> On Thu, 2012-03-15 at 13:23 -0700, Yinghai Lu wrote: >>> On Thu, Mar 15, 2012 at 11:03 AM, Steffen Persvold<sp@numascale.com> >>> wrote: >>>> Use x2apic_supported() in the default_apic_id_valid() function. If >>>> x2apic mode is disabled (via nox2apic for example), >>>> x2apic_supported() will return false. >>>> >>>> This allows us to substitute the check in >>>> arch/x86/kernel/acpi/boot.c::acpi_parse_x2apic and avoid feigning >>>> the x2apic cpu feature in the NumaChip apic code. >>>> >>>> Signed-off-by: Steffen Persvold<sp@numascale.com> >>>> Reviewed-by: Daniel J Blueman<daniel@numascale-asia.com> >>> >>> I double checked on system with x2apic preenabled, >>> nox2apic in boot command line still works well and it >>> skips starting APs with apic id> 255. >>> >>> Acked-by: Yinghai Lu<yinghai@kernel.org> >> > > Suresh, > >> This breaks the smpboot check if enabling interrupt-remapping/x2apic >> fails on a platform. We will be in xapic mode and we don't clear the >> x2apic cpufeature bit in this case and as such smpboot check will fail. >> >> So this change breaks the commit >> c284b42abadbb22083bfde24d308899c08d44ffa. >> > > I was afraid of that. > >> I think the right thing is to have two different apid_id_valid checks >> one for xapic driver (apic_flat_64.c) and another for x2apic driver >> (x2apic_phys/cluster.c) and that way, x2apic MADT entries will be parsed >> only if bios has handed over the OS in x2apic mode or if we have >> selected the numachip model. >> > > Is my understanding of your suggestion correct that in > x2apic_phys/cluster.c we add the following apic_id_valid() function : > > static int x2apic_apic_id_valid(int apicid) > { > return x2apic_mode || (apicid < 255); > } > > ? > > Considering that this function (apic->apic_id_valid()) is called already > in the acpi/boot.c::acpi_parse_x2apic() function is it sufficient enough > to test for x2apic_mode ? Yinghai indicated that x2apic_mode was not set > at this point, thus it was testing cpu_has_x2apic instead ? > > I must admit that I am not familiar enough with the APIC/ACPI code base > to determine the sequence of events here (i.e MADT parsing, enabling of > x2apic mode etc. etc.).
After reading the code a bit more it seems that the sequence is as follows :
kernel/setup.c::setup_arch() calls check_x2apic(). check_x2apic() first checks the cpu feature flag, then checks the MSR_IA32_APICBASE msr to see if bios has enabled x2apic mode. If this is the case, x2apic_preenabled and x2apic_mode is set to 1.
Later on in setup_arch(), the ACPI parsing starts.
My assumption is that the approach suggested in my previous email (based on Suresh' comment) with separate apic_id_valid() functions would be sufficient even for the MADT parsing ?
Kind regards, Steffen
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