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ARM: spectre-v2: per-CPU vtables to work around big.Little systems

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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>
This commit is contained in:
Russell King
2018-07-19 12:21:31 +01:00
parent e209950fdd
commit 383fb3ee80
4 changed files with 61 additions and 15 deletions
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23
arch/arm/include/asm/proc-fns.h
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@@ -104,12 +104,35 @@ extern void cpu_do_resume(void *);
#else
extern struct processor processor;
#if defined(CONFIG_BIG_LITTLE) && defined(CONFIG_HARDEN_BRANCH_PREDICTOR)
#include <linux/smp.h>
/*
* This can't be a per-cpu variable because we need to access it before
* per-cpu has been initialised. We have a couple of functions that are
* called in a pre-emptible context, and so can't use smp_processor_id()
* there, hence PROC_TABLE(). We insist in init_proc_vtable() that the
* function pointers for these are identical across all CPUs.
*/
extern struct processor *cpu_vtable[];
#define PROC_VTABLE(f) cpu_vtable[smp_processor_id()]->f
#define PROC_TABLE(f) cpu_vtable[0]->f
static inline void init_proc_vtable(const struct processor *p)
{
unsigned int cpu = smp_processor_id();
*cpu_vtable[cpu] = *p;
WARN_ON_ONCE(cpu_vtable[cpu]->dcache_clean_area !=
cpu_vtable[0]->dcache_clean_area);
WARN_ON_ONCE(cpu_vtable[cpu]->set_pte_ext !=
cpu_vtable[0]->set_pte_ext);
}
#else
#define PROC_VTABLE(f) processor.f
#define PROC_TABLE(f) processor.f
static inline void init_proc_vtable(const struct processor *p)
{
processor = *p;
}
#endif
#define cpu_proc_init PROC_VTABLE(_proc_init)
#define cpu_check_bugs PROC_VTABLE(check_bugs)