[PATCH v2 05/24] arm64: context switch POR_EL0 register

From: Joey Gouly <joey.gouly@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: akpm@linux-foundation.org, aneesh.kumar@linux.ibm.com,
	broonie@kernel.org, catalin.marinas@arm.com,
	dave.hansen@linux.intel.com, joey.gouly@arm.com, maz@kernel.org,
	oliver.upton@linux.dev, shuah@kernel.org, will@kernel.org,
	kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>
Subject: [PATCH v2 05/24] arm64: context switch POR_EL0 register
Date: Fri, 27 Oct 2023 19:08:31 +0100	[thread overview]
Message-ID: <20231027180850.1068089-6-joey.gouly@arm.com> (raw)
In-Reply-To: <20231027180850.1068089-1-joey.gouly@arm.com>

POR_EL0 is a register that can be modified by userspace directly,
so it must be context switched.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/cpufeature.h |  6 ++++++
 arch/arm64/include/asm/processor.h  |  1 +
 arch/arm64/include/asm/sysreg.h     |  3 +++
 arch/arm64/kernel/process.c         | 19 +++++++++++++++++++
 4 files changed, 29 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 5bba39376055..019af90a3cf4 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -831,6 +831,12 @@ static inline bool system_supports_tlb_range(void)
 		cpus_have_const_cap(ARM64_HAS_TLB_RANGE);
 }
 
+static inline bool system_supports_poe(void)
+{
+	return IS_ENABLED(CONFIG_ARM64_POE) &&
+		alternative_has_cap_unlikely(ARM64_HAS_S1POE);
+}
+
 int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);
 bool try_emulate_mrs(struct pt_regs *regs, u32 isn);
 
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index e5bc54522e71..b3ad719c2d0c 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -179,6 +179,7 @@ struct thread_struct {
 	u64			sctlr_user;
 	u64			svcr;
 	u64			tpidr2_el0;
+	u64			por_el0;
 };
 
 static inline unsigned int thread_get_vl(struct thread_struct *thread,
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index cc2d61fd45c3..32270823a40b 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -1007,6 +1007,9 @@
 #define POE_RXW		UL(0x7)
 #define POE_MASK	UL(0xf)
 
+/* Initial value for Permission Overlay Extension for EL0 */
+#define POR_EL0_INIT	POE_RXW
+
 #define ARM64_FEATURE_FIELD_BITS	4
 
 /* Defined for compatibility only, do not add new users. */
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 0fcc4eb1a7ab..9caed797fc47 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -271,12 +271,19 @@ static void flush_tagged_addr_state(void)
 		clear_thread_flag(TIF_TAGGED_ADDR);
 }
 
+static void flush_poe(void)
+{
+	if (system_supports_poe())
+		write_sysreg_s(POR_EL0_INIT, SYS_POR_EL0);
+}
+
 void flush_thread(void)
 {
 	fpsimd_flush_thread();
 	tls_thread_flush();
 	flush_ptrace_hw_breakpoint(current);
 	flush_tagged_addr_state();
+	flush_poe();
 }
 
 void arch_release_task_struct(struct task_struct *tsk)
@@ -498,6 +505,17 @@ static void erratum_1418040_new_exec(void)
 	preempt_enable();
 }
 
+static void permission_overlay_switch(struct task_struct *next)
+{
+	if (system_supports_poe()) {
+		current->thread.por_el0 = read_sysreg_s(SYS_POR_EL0);
+		if (current->thread.por_el0 != next->thread.por_el0) {
+			write_sysreg_s(next->thread.por_el0, SYS_POR_EL0);
+			isb();
+		}
+	}
+}
+
 /*
  * __switch_to() checks current->thread.sctlr_user as an optimisation. Therefore
  * this function must be called with preemption disabled and the update to
@@ -533,6 +551,7 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	ssbs_thread_switch(next);
 	erratum_1418040_thread_switch(next);
 	ptrauth_thread_switch_user(next);
+	permission_overlay_switch(next);
 
 	/*
 	 * Complete any pending TLB or cache maintenance on this CPU in case
-- 
2.25.1

