[PATCH 3.19 141/175] MIPS: HTW: Prevent accidental HTW start due to nested htw_{start, stop}

Greg Kroah-Hartman
2015-03-04T06:24:14Z

From: Markos Chandras <markos.chandras@imgtec.com>

commit ed4cbc81addbc076b016c5b979fd1a02f0897f0a upstream.

activate_mm() and switch_mm() call get_new_mmu_context() which in turn
can enable the HTW before the entryhi is changed with the new ASID.
Since the latter will enable the HTW in local_flush_tlb_all(),
then there is a small timing window where the HTW is running with the
new ASID but with an old pgd since the TLBMISS_HANDLER_SETUP_PGD
hasn't assigned a new one yet. In order to prevent that, we introduce a
simple htw counter to avoid starting HTW accidentally due to nested
htw_{start,stop}() sequences. Moreover, since various IPI calls can
enforce TLB flushing operations on a different core, such an operation
may interrupt another htw_{stop,start} in progress leading inconsistent
updates of the htw_seq variable. In order to avoid that, we disable the
interrupts whenever we update that variable.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9118/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/mips/include/asm/cpu-info.h | 5 +++++
arch/mips/include/asm/mmu_context.h | 7 ++++++-
arch/mips/include/asm/pgtable.h | 24 ++++++++++++++++++------
arch/mips/kernel/cpu-probe.c | 4 +++-
4 files changed, 32 insertions(+), 8 deletions(-)

--- a/arch/mips/include/asm/cpu-info.h
+++ b/arch/mips/include/asm/cpu-info.h
@@ -84,6 +84,11 @@ struct cpuinfo_mips {
* (shifted by _CACHE_SHIFT)
*/
unsigned int writecombine;
+ /*
+ * Simple counter to prevent enabling HTW in nested
+ * htw_start/htw_stop calls
+ */
+ unsigned int htw_seq;
} __attribute__((aligned(SMP_CACHE_BYTES)));

extern struct cpuinfo_mips cpu_data[];
--- a/arch/mips/include/asm/mmu_context.h
+++ b/arch/mips/include/asm/mmu_context.h
@@ -25,7 +25,6 @@ do { \
if (cpu_has_htw) { \
write_c0_pwbase(pgd); \
back_to_back_c0_hazard(); \
- htw_reset(); \
} \
} while (0)

@@ -142,6 +141,7 @@ static inline void switch_mm(struct mm_s
unsigned long flags;
local_irq_save(flags);

+ htw_stop();
/* Check if our ASID is of an older version and thus invalid */
if ((cpu_context(cpu, next) ^ asid_cache(cpu)) & ASID_VERSION_MASK)
get_new_mmu_context(next, cpu);
@@ -154,6 +154,7 @@ static inline void switch_mm(struct mm_s
*/
cpumask_clear_cpu(cpu, mm_cpumask(prev));
cpumask_set_cpu(cpu, mm_cpumask(next));
+ htw_start();

local_irq_restore(flags);
}
@@ -180,6 +181,7 @@ activate_mm(struct mm_struct *prev, stru

local_irq_save(flags);

+ htw_stop();
/* Unconditionally get a new ASID. */
get_new_mmu_context(next, cpu);

@@ -189,6 +191,7 @@ activate_mm(struct mm_struct *prev, stru
/* mark mmu ownership change */
cpumask_clear_cpu(cpu, mm_cpumask(prev));
cpumask_set_cpu(cpu, mm_cpumask(next));
+ htw_start();

local_irq_restore(flags);
}
@@ -203,6 +206,7 @@ drop_mmu_context(struct mm_struct *mm, u
unsigned long flags;

local_irq_save(flags);
+ htw_stop();

if (cpumask_test_cpu(cpu, mm_cpumask(mm))) {
get_new_mmu_context(mm, cpu);
@@ -211,6 +215,7 @@ drop_mmu_context(struct mm_struct *mm, u
/* will get a new context next time */
cpu_context(cpu, mm) = 0;
}
+ htw_start();
local_irq_restore(flags);
}

--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -99,19 +99,31 @@ extern void paging_init(void);

#define htw_stop() \
do { \
+ unsigned long flags; \
+ \
if (cpu_has_htw) { \
- write_c0_pwctl(read_c0_pwctl() & \
- ~(1 << MIPS_PWCTL_PWEN_SHIFT)); \
- back_to_back_c0_hazard(); \
+ local_irq_save(flags); \
+ if(!raw_current_cpu_data.htw_seq++) { \
+ write_c0_pwctl(read_c0_pwctl() & \
+ ~(1 << MIPS_PWCTL_PWEN_SHIFT)); \
+ back_to_back_c0_hazard(); \
+ } \
+ local_irq_restore(flags); \
} \
} while(0)

#define htw_start() \
do { \
+ unsigned long flags; \
+ \
if (cpu_has_htw) { \
- write_c0_pwctl(read_c0_pwctl() | \
- (1 << MIPS_PWCTL_PWEN_SHIFT)); \
- back_to_back_c0_hazard(); \
+ local_irq_save(flags); \
+ if (!--raw_current_cpu_data.htw_seq) { \
+ write_c0_pwctl(read_c0_pwctl() | \
+ (1 << MIPS_PWCTL_PWEN_SHIFT)); \
+ back_to_back_c0_hazard(); \
+ } \
+ local_irq_restore(flags); \
} \
} while(0)

--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -424,8 +424,10 @@ static inline unsigned int decode_config
if (config3 & MIPS_CONF3_MSA)
c->ases |= MIPS_ASE_MSA;
/* Only tested on 32-bit cores */
- if ((config3 & MIPS_CONF3_PW) && config_enabled(CONFIG_32BIT))
+ if ((config3 & MIPS_CONF3_PW) && config_enabled(CONFIG_32BIT)) {
+ c->htw_seq = 0;
c->options |= MIPS_CPU_HTW;
+ }

return config3 & MIPS_CONF_M;
}