Having both VHE and non-VHE capable CPUs in the same system
is likely to be a recipe for disaster.
If the boot CPU has VHE, but a secondary is not, we won't be
able to downgrade and run the kernel at EL1. Add CPU hotplug
to the mix, and this produces a terrifying mess.
Let's solve the problem once and for all. If you mix VHE and
non-VHE CPUs in the same system, you deserve to loose, and this
patch makes sure you don't get a chance.
This is implemented by storing the kernel execution level in
a global variable. Secondaries will park themselves in a
WFI loop if they observe a mismatch. Also, the primary CPU
will detect that the secondary CPU has died on a mismatched
execution level. Panic will follow.
Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
---
arch/arm64/include/asm/virt.h | 15 +++++++++++++++
arch/arm64/kernel/head.S | 15 +++++++++++++++
arch/arm64/kernel/smp.c | 4 ++++
3 files changed, 34 insertions(+)
diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index 9f22dd6..8e246f7 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h
@@ -36,6 +36,11 @@
*/
extern u32 __boot_cpu_mode[2];
+/*
+ * __run_cpu_mode records the mode the boot CPU uses for the kernel.
+ */
+extern u32 __run_cpu_mode;
+
void __hyp_set_vectors(phys_addr_t phys_vector_base);
phys_addr_t __hyp_get_vectors(void);
@@ -60,6 +65,16 @@ static inline bool is_kernel_in_hyp_mode(void)
return el == CurrentEL_EL2;
}
+static inline bool is_kernel_mode_mismatched(void)
+{
+ u64 el;
+ u32 mode;
+
+ asm("mrs %0, CurrentEL" : "=r" (el));
+ mode = ACCESS_ONCE(__run_cpu_mode);
+ return el != mode;
+}
+
/* The section containing the hypervisor text */
extern char __hyp_text_start[];
extern char __hyp_text_end[];
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index a179747..318e69f 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -578,7 +578,20 @@ ENTRY(set_cpu_boot_mode_flag)
1: str w20, [x1] // This CPU has booted in EL1
dmb sy
dc ivac, x1 // Invalidate potentially stale cache line
+ adr_l x1, __run_cpu_mode
+ ldr w0, [x1]
+ mrs x20, CurrentEL
+ str w20, [x1]
+ dmb sy
+ dc ivac, x1 // Invalidate potentially stale cache line
+ cbz x0, skip_el_check
+ cmp x0, x20
+ bne mismatched_el
+skip_el_check:
ret
+mismatched_el:
+ wfi
+ b mismatched_el
ENDPROC(set_cpu_boot_mode_flag)
/*
@@ -593,6 +606,8 @@ ENDPROC(set_cpu_boot_mode_flag)
ENTRY(__boot_cpu_mode)
.long BOOT_CPU_MODE_EL2
.long BOOT_CPU_MODE_EL1
+ENTRY(__run_cpu_mode)
+ .long 0
.popsection
#ifdef CONFIG_SMP
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 695801a..b467f51 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -52,6 +52,7 @@
#include <asm/sections.h>
#include <asm/tlbflush.h>
#include <asm/ptrace.h>
+#include <asm/virt.h>
#define CREATE_TRACE_POINTS
#include <trace/events/ipi.h>
@@ -112,6 +113,9 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
pr_crit("CPU%u: failed to come online\n", cpu);
ret = -EIO;
}
+
+ if (is_kernel_mode_mismatched())
+ panic("CPU%u: incompatible execution level", cpu);
} else {
pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
}
--
2.1.4
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