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SubjectRe: [PATCH 01/10] x86/apic: Install an empty physflat_init_apic_ldr
On Thu, 16 Nov 2017, Jan Kiszka wrote:

> From: Jan Kiszka <jan.kiszka@siemens.com>
>
> As the comment already stated, there is no need for setting up LDR in

I prefer to have a proper reference to documentation why this is not
needed than to a comment which is technically dubious.

> physflat mode as it remains unused. flat_init_apic_ldr only served as a
> placeholder for a nop operation so far, causing no harm.
>
> That will change when running over the Jailhouse hypervisor. Here we
> must not touch LDR in a way that destroys the mapping originally set up
> by the Linux root cell. Jailhouse enforces this setting in order to
> efficiently validate any IPI requests sent by a cell.
>
> Avoid a needless clash caused by flat_init_apic_ldr by installing a true
> nop handler.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> arch/x86/kernel/apic/apic_flat_64.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/apic/apic_flat_64.c b/arch/x86/kernel/apic/apic_flat_64.c
> index aa85690e9b64..34bfdfe29a04 100644
> --- a/arch/x86/kernel/apic/apic_flat_64.c
> +++ b/arch/x86/kernel/apic/apic_flat_64.c
> @@ -218,6 +218,11 @@ static int physflat_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
> return 0;
> }
>
> +void physflat_init_apic_ldr(void)

static ?

> +{
> + /* LDR is not used in physflat mode. */

flat_init_apic_ldr() also fiddles with DFR ...

> +}
> +
> static void physflat_send_IPI_allbutself(int vector)
> {
> default_send_IPI_mask_allbutself_phys(cpu_online_mask, vector);
> @@ -251,8 +256,7 @@ static struct apic apic_physflat __ro_after_init = {
> .dest_logical = 0,
> .check_apicid_used = NULL,
>
> - /* not needed, but shouldn't hurt: */
> - .init_apic_ldr = flat_init_apic_ldr,
> + .init_apic_ldr = physflat_init_apic_ldr,
>
> .ioapic_phys_id_map = NULL,
> .setup_apic_routing = NULL,
> --
> 2.12.3
>
>

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