linux-kernel - [PATCH 01/10] x86/apic: Install an empty physflat_init_apic

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Message-Id: <7476b80e275c27beb7d30d564c55966d66d1a825.1510817211.git.jan.kiszka@siemens.com>
Date:   Thu, 16 Nov 2017 08:26:43 +0100
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     x86@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        jailhouse-dev@...glegroups.com
Subject: [PATCH 01/10] x86/apic: Install an empty physflat_init_apic_ldr

From: Jan Kiszka <jan.kiszka@...mens.com>

As the comment already stated, there is no need for setting up LDR in
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@...mens.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)
+{
+	/* LDR is not used in physflat mode. */
+}
+
 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