ARM: spectre-v2: per-CPU vtables to work around big.Little systems
In big.Little systems, some CPUs require the Spectre workarounds in
paths such as the context switch, but other CPUs do not. In order
to handle these differences, we need per-CPU vtables.
We are unable to use the kernel's per-CPU variables to support this
as per-CPU is not initialised at times when we need access to the
vtables, so we have to use an array indexed by logical CPU number.
We use an array-of-pointers to avoid having function pointers in
the kernel's read/write .data section.
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 5ad0b67..82b879d 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -42,6 +42,7 @@
#include <asm/mmu_context.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
+#include <asm/procinfo.h>
#include <asm/processor.h>
#include <asm/sections.h>
#include <asm/tlbflush.h>
@@ -102,6 +103,30 @@
#endif
}
+#if defined(CONFIG_BIG_LITTLE) && defined(CONFIG_HARDEN_BRANCH_PREDICTOR)
+static int secondary_biglittle_prepare(unsigned int cpu)
+{
+ if (!cpu_vtable[cpu])
+ cpu_vtable[cpu] = kzalloc(sizeof(*cpu_vtable[cpu]), GFP_KERNEL);
+
+ return cpu_vtable[cpu] ? 0 : -ENOMEM;
+}
+
+static void secondary_biglittle_init(void)
+{
+ init_proc_vtable(lookup_processor(read_cpuid_id())->proc);
+}
+#else
+static int secondary_biglittle_prepare(unsigned int cpu)
+{
+ return 0;
+}
+
+static void secondary_biglittle_init(void)
+{
+}
+#endif
+
int __cpu_up(unsigned int cpu, struct task_struct *idle)
{
int ret;
@@ -109,6 +134,10 @@
if (!smp_ops.smp_boot_secondary)
return -ENOSYS;
+ ret = secondary_biglittle_prepare(cpu);
+ if (ret)
+ return ret;
+
/*
* We need to tell the secondary core where to find
* its stack and the page tables.
@@ -360,6 +389,8 @@
struct mm_struct *mm = &init_mm;
unsigned int cpu;
+ secondary_biglittle_init();
+
/*
* The identity mapping is uncached (strongly ordered), so
* switch away from it before attempting any exclusive accesses.