linux-kernel - [PATCH v2 6/6] arm64: Ensure the secondary CPUs have safe ASIDBits size

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Date:	Tue,  1 Dec 2015 15:12:11 +0000
From:	"Suzuki K. Poulose" <suzuki.poulose@....com>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	marc.zyngier@....com, linux-kernel@...r.kernel.org,
	mark.rutland@....com, will.deacon@....com, catalin.marinas@....com,
	"Suzuki K. Poulose" <suzuki.poulose@....com>
Subject: [PATCH v2 6/6] arm64: Ensure the secondary CPUs have safe ASIDBits size

The ID_AA64MMFR0_EL1:ASIDBits determines the size of the mm context
id and is used in the early boot to make decisions. The value is
picked up from the Boot CPU and cannot be delayed until other CPUs
are up. If a secondary CPU has a smaller size than that of the Boot
CPU, things will break horribly and the usual SANITY check is not good
enough to prevent the system from crashing. Prevent this by failing CPUs with
ASID smaller than that of the boot CPU.

Cc: Will Deacon <will.deacon@....com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Suzuki K. Poulose <suzuki.poulose@....com>
---
 arch/arm64/include/asm/mmu_context.h |    2 ++
 arch/arm64/kernel/cpufeature.c       |    2 ++
 arch/arm64/mm/context.c              |   14 ++++++++++++++
 3 files changed, 18 insertions(+)

diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index 2416578..bd8a0b9 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -147,4 +147,6 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 #define deactivate_mm(tsk,mm)	do { } while (0)
 #define activate_mm(prev,next)	switch_mm(prev, next, NULL)
 
+void verify_cpu_asid_bits(void);
+
 #endif
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 8dd05283..76bb988 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -24,6 +24,7 @@
 #include <asm/cpu.h>
 #include <asm/cpufeature.h>
 #include <asm/cpu_ops.h>
+#include <asm/mmu_context.h>
 #include <asm/processor.h>
 #include <asm/sysreg.h>
 
@@ -829,6 +830,7 @@ static u64 __raw_read_system_reg(u32 sys_id)
  */
 static void check_early_cpu_features(void)
 {
+	verify_cpu_asid_bits();
 }
 
 /*
diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index 643bf4b..3d75c2f 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -24,6 +24,7 @@
 
 #include <asm/cpufeature.h>
 #include <asm/mmu_context.h>
+#include <asm/smp.h>
 #include <asm/tlbflush.h>
 
 static u32 asid_bits;
@@ -62,6 +63,19 @@ static u32 get_cpu_asid_bits(void)
 	return asid;
 }
 
+/* Check if the current cpu's ASIDBits is compatible with asid_bits */
+void verify_cpu_asid_bits(void)
+{
+	u32 asid = get_cpu_asid_bits();
+
+	if (asid < asid_bits) {
+		/* Kill the CPU */
+		pr_crit("CPU%d: has smaller ASIDBits(%u) than the one in use (%u)\n",
+				smp_processor_id(), asid, asid_bits);
+		kill_cpu_early();
+	}
+}
+
 static void flush_context(unsigned int cpu)
 {
 	int i;
-- 
1.7.9.5

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