On 5/28/20 11:37 PM, Dexuan Cui wrote:
> 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 becauase 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,
> and 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.
>
> IMHO the patch is safe because the current default algorithm to choose
> the apic driver is unchanged; the patch makes a difference only when
> the user specifies the apic= kernel parameter, e.g. "apic=physical flat".
>
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> ---
> arch/x86/kernel/apic/apic_flat_64.c | 27 ++++++++++++++++++++++++++-
> 1 file changed, 26 insertions(+), 1 deletion(-)
Hi,
Looks like you will also need to update
Documentation/admin-guide/kernel-parameters.txt, where it says:
For X86-32, this can also be used to specify an APIC
driver name.
> diff --git a/arch/x86/kernel/apic/apic_flat_64.c b/arch/x86/kernel/apic/apic_flat_64.c
> index 7862b152a052..efbec63bb01f 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 cmdline_apic __initdata;
> +static int __init parse_apic(char *arg)
> +{
> + 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 flat_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
> {
> - return 1;
> + if (!cmdline_apic)
> + return 1;
> +
> + return apic == &apic_flat;
> }
>
> /*
>
--
~Randy
