parse_apic() allows the user to try a different APIC driver than the default one that's automatically chosen. It works for X86-32, but doesn't work for X86-64 because it was removed in 2009 for X86-64 by commit 7b38725318f4 ("x86: remove subarchitecture support code"), whose changelog doesn't explicitly describe the removal for X86-64. The patch adds back the functionality for X86-64. The intent is mainly to work around an APIC emulation bug in Hyper-V in the case of kdump: currently Hyper-V does not honor the disabled state of the local APICs, so all the IOAPIC-based interrupts may not be delivered to the correct virtual CPU, if the logical-mode APIC driver is used (the kdump kernel usually uses the logical-mode APIC driver, since typically only 1 CPU is active). Luckily the kdump issue can be worked around by forcing the kdump kernel to use physical mode, before the fix to Hyper-V becomes widely available. The current algorithm of choosing an APIC driver is: 1. The global pointer "struct apic *apic" has a default value, i.e "apic_default" on X86-32, and "apic_flat" on X86-64. 2. If the early_param "apic=" is specified, parse_apic() is called and the pointer "apic" is changed if a matching APIC driver is found. 3. default_acpi_madt_oem_check() calls the acpi_madt_oem_check() method of all APIC drivers, which may override the "apic" pointer. 4. default_setup_apic_routing() may override the "apic" pointer, e.g. by calling the probe() method of all APIC drivers. Note: refer to the order of the APIC drivers specified in arch/x86/kernel/apic/Makefile. The patch is safe because if the apic= early param is not specified, the current algorithm of choosing an APIC driver is unchanged; when the param is specified (e.g. on X86-64, "apic=physical flat"), the kernel still tries to find a "more suitable" APIC driver in the above step 3 and 4: e.g. if the BIOS/firmware requires that apic_x2apic_phys should be used, the above step 4 will override the APIC driver to apic_x2apic_phys, even if an early_param "apic=physical flat" is specified. On Hyper-V, when a Linux VM has <= 8 virtual CPUs, if we use "apic=physical flat", sending IPIs to multiple vCPUs is still fast because Linux VM uses the para-virtualized IPI hypercalls: see hv_apic_init(). The patch adds the __init tag for flat_acpi_madt_oem_check() and physflat_acpi_madt_oem_check() to avoid a warning seen with "make W=1": flat_acpi_madt_oem_check() accesses cmdline_apic, which has a __initdata tag. Fixes: 7b38725318f4 ("x86: remove subarchitecture support code") Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx> --- Changes in v2 (5/28/2020): Updated Documentation/admin-guide/kernel-parameters.txt. [Randy Dunlap] Changed apic_set_verbosity(). Enhanced the changelog. Changes in v3 (5/31/2020): Added the __init tag for flat_acpi_madt_oem_check() and physflat_acpi_madt_oem_check() to avoid a warning seen with "make W=1". (Thanks to kbuild test robot <lkp@xxxxxxxxx>). Updated the changelog for the __init tag. Today is 6/26/2020 and this is just a RESEND of v3, which was posted on 5/31 (https://lkml.org/lkml/2020/5/31/198). .../admin-guide/kernel-parameters.txt | 11 +++++-- arch/x86/kernel/apic/apic.c | 11 +++---- arch/x86/kernel/apic/apic_flat_64.c | 31 +++++++++++++++++-- 3 files changed, 40 insertions(+), 13 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 7bc83f3d9bdf..c4503fff9348 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -341,10 +341,15 @@ Format: { quiet (default) | verbose | debug } Change the amount of debugging information output when initialising the APIC and IO-APIC components. - For X86-32, this can also be used to specify an APIC - driver name. + This can also be used to specify an APIC driver name. Format: apic=driver_name - Examples: apic=bigsmp + Examples: + On X86-32: apic=bigsmp + On X86-64: "apic=physical flat" + Note: the available driver names depend on the + architecture and the kernel config; the setting may + be overridden by the acpi_madt_oem_check() and probe() + methods of other APIC drivers. apic_extnmi= [APIC,X86] External NMI delivery setting Format: { bsp (default) | all | none } diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c index e53dda210cd7..6f7d75b6358b 100644 --- a/arch/x86/kernel/apic/apic.c +++ b/arch/x86/kernel/apic/apic.c @@ -2855,13 +2855,10 @@ static int __init apic_set_verbosity(char *arg) apic_verbosity = APIC_DEBUG; else if (strcmp("verbose", arg) == 0) apic_verbosity = APIC_VERBOSE; -#ifdef CONFIG_X86_64 - else { - pr_warn("APIC Verbosity level %s not recognised" - " use apic=verbose or apic=debug\n", arg); - return -EINVAL; - } -#endif + + /* Ignore unrecognized verbosity level setting. */ + + pr_info("APIC Verbosity level is %d\n", apic_verbosity); return 0; } diff --git a/arch/x86/kernel/apic/apic_flat_64.c b/arch/x86/kernel/apic/apic_flat_64.c index 7862b152a052..da8f3640453f 100644 --- a/arch/x86/kernel/apic/apic_flat_64.c +++ b/arch/x86/kernel/apic/apic_flat_64.c @@ -23,9 +23,34 @@ static struct apic apic_flat; struct apic *apic __ro_after_init = &apic_flat; EXPORT_SYMBOL_GPL(apic); -static int flat_acpi_madt_oem_check(char *oem_id, char *oem_table_id) +static int cmdline_apic __initdata; +static int __init parse_apic(char *arg) { - return 1; + struct apic **drv; + + if (!arg) + return -EINVAL; + + for (drv = __apicdrivers; drv < __apicdrivers_end; drv++) { + if (!strcmp((*drv)->name, arg)) { + apic = *drv; + cmdline_apic = 1; + return 0; + } + } + + /* Parsed again by __setup for debug/verbose */ + return 0; +} +early_param("apic", parse_apic); + + +static int __init flat_acpi_madt_oem_check(char *oem_id, char *oem_table_id) +{ + if (!cmdline_apic) + return 1; + + return apic == &apic_flat; } /* @@ -157,7 +182,7 @@ static struct apic apic_flat __ro_after_init = { * We cannot use logical delivery in this case because the mask * overflows, so use physical mode. */ -static int physflat_acpi_madt_oem_check(char *oem_id, char *oem_table_id) +static int __init physflat_acpi_madt_oem_check(char *oem_id, char *oem_table_id) { #ifdef CONFIG_ACPI /* -- 2.19.1