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Subject[PATCH 4.19 030/276] arm64: errata: Add workaround for Cortex-A76 erratum #1463225
Date
From: Will Deacon <will.deacon@arm.com>

commit 969f5ea627570e91c9d54403287ee3ed657f58fe upstream.

Revisions of the Cortex-A76 CPU prior to r4p0 are affected by an erratum
that can prevent interrupts from being taken when single-stepping.

This patch implements a software workaround to prevent userspace from
effectively being able to disable interrupts.

Cc: <stable@vger.kernel.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>


---
Documentation/arm64/silicon-errata.txt | 1
arch/arm64/Kconfig | 18 ++++++++++++++++
arch/arm64/include/asm/cpucaps.h | 3 +-
arch/arm64/include/asm/cputype.h | 2 +
arch/arm64/kernel/cpu_errata.c | 24 +++++++++++++++++++++
arch/arm64/kernel/syscall.c | 31 +++++++++++++++++++++++++++
arch/arm64/mm/fault.c | 37 +++++++++++++++++++++++++++++++--
7 files changed, 113 insertions(+), 3 deletions(-)

--- a/Documentation/arm64/silicon-errata.txt
+++ b/Documentation/arm64/silicon-errata.txt
@@ -58,6 +58,7 @@ stable kernels.
| ARM | Cortex-A72 | #853709 | N/A |
| ARM | Cortex-A73 | #858921 | ARM64_ERRATUM_858921 |
| ARM | Cortex-A55 | #1024718 | ARM64_ERRATUM_1024718 |
+| ARM | Cortex-A76 | #1463225 | ARM64_ERRATUM_1463225 |
| ARM | MMU-500 | #841119,#826419 | N/A |
| | | | |
| Cavium | ThunderX ITS | #22375, #24313 | CAVIUM_ERRATUM_22375 |
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -479,6 +479,24 @@ config ARM64_ERRATUM_1024718

If unsure, say Y.

+config ARM64_ERRATUM_1463225
+ bool "Cortex-A76: Software Step might prevent interrupt recognition"
+ default y
+ help
+ This option adds a workaround for Arm Cortex-A76 erratum 1463225.
+
+ On the affected Cortex-A76 cores (r0p0 to r3p1), software stepping
+ of a system call instruction (SVC) can prevent recognition of
+ subsequent interrupts when software stepping is disabled in the
+ exception handler of the system call and either kernel debugging
+ is enabled or VHE is in use.
+
+ Work around the erratum by triggering a dummy step exception
+ when handling a system call from a task that is being stepped
+ in a VHE configuration of the kernel.
+
+ If unsure, say Y.
+
config CAVIUM_ERRATUM_22375
bool "Cavium erratum 22375, 24313"
default y
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -51,7 +51,8 @@
#define ARM64_SSBD 30
#define ARM64_MISMATCHED_CACHE_TYPE 31
#define ARM64_HAS_STAGE2_FWB 32
+#define ARM64_WORKAROUND_1463225 33

-#define ARM64_NCAPS 33
+#define ARM64_NCAPS 34

#endif /* __ASM_CPUCAPS_H */
--- a/arch/arm64/include/asm/cputype.h
+++ b/arch/arm64/include/asm/cputype.h
@@ -86,6 +86,7 @@
#define ARM_CPU_PART_CORTEX_A75 0xD0A
#define ARM_CPU_PART_CORTEX_A35 0xD04
#define ARM_CPU_PART_CORTEX_A55 0xD05
+#define ARM_CPU_PART_CORTEX_A76 0xD0B

#define APM_CPU_PART_POTENZA 0x000

@@ -110,6 +111,7 @@
#define MIDR_CORTEX_A75 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A75)
#define MIDR_CORTEX_A35 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A35)
#define MIDR_CORTEX_A55 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A55)
+#define MIDR_CORTEX_A76 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A76)
#define MIDR_THUNDERX MIDR_CPU_MODEL(ARM_CPU_IMP_CAVIUM, CAVIUM_CPU_PART_THUNDERX)
#define MIDR_THUNDERX_81XX MIDR_CPU_MODEL(ARM_CPU_IMP_CAVIUM, CAVIUM_CPU_PART_THUNDERX_81XX)
#define MIDR_THUNDERX_83XX MIDR_CPU_MODEL(ARM_CPU_IMP_CAVIUM, CAVIUM_CPU_PART_THUNDERX_83XX)
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -411,6 +411,22 @@ static bool has_ssbd_mitigation(const st
}
#endif /* CONFIG_ARM64_SSBD */

+#ifdef CONFIG_ARM64_ERRATUM_1463225
+DEFINE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa);
+
+static bool
+has_cortex_a76_erratum_1463225(const struct arm64_cpu_capabilities *entry,
+ int scope)
+{
+ u32 midr = read_cpuid_id();
+ /* Cortex-A76 r0p0 - r3p1 */
+ struct midr_range range = MIDR_RANGE(MIDR_CORTEX_A76, 0, 0, 3, 1);
+
+ WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
+ return is_midr_in_range(midr, &range) && is_kernel_in_hyp_mode();
+}
+#endif
+
#define CAP_MIDR_RANGE(model, v_min, r_min, v_max, r_max) \
.matches = is_affected_midr_range, \
.midr_range = MIDR_RANGE(model, v_min, r_min, v_max, r_max)
@@ -680,6 +696,14 @@ const struct arm64_cpu_capabilities arm6
.matches = has_ssbd_mitigation,
},
#endif
+#ifdef CONFIG_ARM64_ERRATUM_1463225
+ {
+ .desc = "ARM erratum 1463225",
+ .capability = ARM64_WORKAROUND_1463225,
+ .type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,
+ .matches = has_cortex_a76_erratum_1463225,
+ },
+#endif
{
}
};
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -8,6 +8,7 @@
#include <linux/syscalls.h>

#include <asm/daifflags.h>
+#include <asm/debug-monitors.h>
#include <asm/fpsimd.h>
#include <asm/syscall.h>
#include <asm/thread_info.h>
@@ -60,6 +61,35 @@ static inline bool has_syscall_work(unsi
int syscall_trace_enter(struct pt_regs *regs);
void syscall_trace_exit(struct pt_regs *regs);

+#ifdef CONFIG_ARM64_ERRATUM_1463225
+DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa);
+
+static void cortex_a76_erratum_1463225_svc_handler(void)
+{
+ u32 reg, val;
+
+ if (!unlikely(test_thread_flag(TIF_SINGLESTEP)))
+ return;
+
+ if (!unlikely(this_cpu_has_cap(ARM64_WORKAROUND_1463225)))
+ return;
+
+ __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 1);
+ reg = read_sysreg(mdscr_el1);
+ val = reg | DBG_MDSCR_SS | DBG_MDSCR_KDE;
+ write_sysreg(val, mdscr_el1);
+ asm volatile("msr daifclr, #8");
+ isb();
+
+ /* We will have taken a single-step exception by this point */
+
+ write_sysreg(reg, mdscr_el1);
+ __this_cpu_write(__in_cortex_a76_erratum_1463225_wa, 0);
+}
+#else
+static void cortex_a76_erratum_1463225_svc_handler(void) { }
+#endif /* CONFIG_ARM64_ERRATUM_1463225 */
+
static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
const syscall_fn_t syscall_table[])
{
@@ -68,6 +98,7 @@ static void el0_svc_common(struct pt_reg
regs->orig_x0 = regs->regs[0];
regs->syscallno = scno;

+ cortex_a76_erratum_1463225_svc_handler();
local_daif_restore(DAIF_PROCCTX);
user_exit();

--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -827,14 +827,47 @@ void __init hook_debug_fault_code(int nr
debug_fault_info[nr].name = name;
}

+#ifdef CONFIG_ARM64_ERRATUM_1463225
+DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa);
+
+static int __exception
+cortex_a76_erratum_1463225_debug_handler(struct pt_regs *regs)
+{
+ if (user_mode(regs))
+ return 0;
+
+ if (!__this_cpu_read(__in_cortex_a76_erratum_1463225_wa))
+ return 0;
+
+ /*
+ * We've taken a dummy step exception from the kernel to ensure
+ * that interrupts are re-enabled on the syscall path. Return back
+ * to cortex_a76_erratum_1463225_svc_handler() with debug exceptions
+ * masked so that we can safely restore the mdscr and get on with
+ * handling the syscall.
+ */
+ regs->pstate |= PSR_D_BIT;
+ return 1;
+}
+#else
+static int __exception
+cortex_a76_erratum_1463225_debug_handler(struct pt_regs *regs)
+{
+ return 0;
+}
+#endif /* CONFIG_ARM64_ERRATUM_1463225 */
+
asmlinkage int __exception do_debug_exception(unsigned long addr_if_watchpoint,
- unsigned int esr,
- struct pt_regs *regs)
+ unsigned int esr,
+ struct pt_regs *regs)
{
const struct fault_info *inf = debug_fault_info + DBG_ESR_EVT(esr);
unsigned long pc = instruction_pointer(regs);
int rv;

+ if (cortex_a76_erratum_1463225_debug_handler(regs))
+ return 0;
+
/*
* Tell lockdep we disabled irqs in entry.S. Do nothing if they were
* already disabled to preserve the last enabled/disabled addresses.

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