Message-Id: <20230418194746.620266-1-scott@os.amperecomputing.com>
Date:   Tue, 18 Apr 2023 12:47:45 -0700
From:   D Scott Phillips <scott@...amperecomputing.com>
To:     linux-arm-kernel@...ts.infradead.org,
        James Morse <james.morse@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 RESEND 1/2] arm64: sdei: Use alternative patching to select the conduit in sdei exit

Patch in the conduit instruction for SDEI instead of branching between the
possible conduits. The sdei driver's conduit initialization is moved
earlier in the initialization flow, into setup_arch(), so that it is ready
in time for alternative patching.

Suggested-by: James Morse <james.morse@....com>
Signed-off-by: D Scott Phillips <scott@...amperecomputing.com>
---
 arch/arm64/include/asm/sdei.h | 13 +++----
 arch/arm64/kernel/entry.S     | 26 ++++++-------
 arch/arm64/kernel/sdei.c      | 30 ++++++++++++---
 arch/arm64/kernel/setup.c     |  3 ++
 drivers/firmware/arm_sdei.c   | 71 +++++++++++++++++++----------------
 include/linux/arm_sdei.h      |  6 ++-
 6 files changed, 88 insertions(+), 61 deletions(-)

diff --git a/arch/arm64/include/asm/sdei.h b/arch/arm64/include/asm/sdei.h
index 4292d9bafb9d..badb39510515 100644
--- a/arch/arm64/include/asm/sdei.h
+++ b/arch/arm64/include/asm/sdei.h
@@ -3,10 +3,6 @@
 #ifndef __ASM_SDEI_H
 #define __ASM_SDEI_H
 
-/* Values for sdei_exit_mode */
-#define SDEI_EXIT_HVC  0
-#define SDEI_EXIT_SMC  1
-
 #define SDEI_STACK_SIZE		IRQ_STACK_SIZE
 
 #ifndef __ASSEMBLY__
@@ -17,8 +13,6 @@
 
 #include <asm/virt.h>
 
-extern unsigned long sdei_exit_mode;
-
 /* Software Delegated Exception entry point from firmware*/
 asmlinkage void __sdei_asm_handler(unsigned long event_num, unsigned long arg,
 				   unsigned long pc, unsigned long pstate);
@@ -40,8 +34,11 @@ asmlinkage unsigned long __sdei_handler(struct pt_regs *regs,
 unsigned long do_sdei_event(struct pt_regs *regs,
 			    struct sdei_registered_event *arg);
 
-unsigned long sdei_arch_get_entry_point(int conduit);
-#define sdei_arch_get_entry_point(x)	sdei_arch_get_entry_point(x)
+unsigned long sdei_arch_get_entry_point(void);
+#define sdei_arch_get_entry_point	sdei_arch_get_entry_point
+
+void __init sdei_patch_conduit(struct alt_instr *alt, __le32 *origptr,
+			       __le32 *updptr, int nr_inst);
 
 #endif /* __ASSEMBLY__ */
 #endif	/* __ASM_SDEI_H */
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index ab2a6e33c052..ae7aa02f0df5 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -914,13 +914,10 @@ NOKPROBE(call_on_irq_stack)
 #include <asm/sdei.h>
 #include <uapi/linux/arm_sdei.h>
 
-.macro sdei_handler_exit exit_mode
-	/* On success, this call never returns... */
-	cmp	\exit_mode, #SDEI_EXIT_SMC
-	b.ne	99f
-	smc	#0
-	b	.
-99:	hvc	#0
+.macro sdei_handler_exit
+alternative_cb	ARM64_ALWAYS_SYSTEM, sdei_patch_conduit
+	nop	// Patched to SMC/HVC #0
+alternative_cb_end
 	b	.
 .endm
 
@@ -955,7 +952,6 @@ NOKPROBE(__sdei_asm_entry_trampoline)
  * Make the exit call and restore the original ttbr1_el1
  *
  * x0 & x1: setup for the exit API call
- * x2: exit_mode
  * x4: struct sdei_registered_event argument from registration time.
  */
 SYM_CODE_START(__sdei_asm_exit_trampoline)
@@ -964,7 +960,7 @@ SYM_CODE_START(__sdei_asm_exit_trampoline)
 
 	tramp_unmap_kernel	tmp=x4
 
-1:	sdei_handler_exit exit_mode=x2
+1:	sdei_handler_exit
 SYM_CODE_END(__sdei_asm_exit_trampoline)
 NOKPROBE(__sdei_asm_exit_trampoline)
 .popsection		// .entry.tramp.text
@@ -1070,14 +1066,16 @@ SYM_CODE_START(__sdei_asm_handler)
 	mov_q	x3, SDEI_1_0_FN_SDEI_EVENT_COMPLETE_AND_RESUME
 	csel	x0, x2, x3, ls
 
-	ldr_l	x2, sdei_exit_mode
-
-alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0
-	sdei_handler_exit exit_mode=x2
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+alternative_if ARM64_UNMAP_KERNEL_AT_EL0
+	b 1f
 alternative_else_nop_endif
+#endif
+
+	sdei_handler_exit
 
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
-	tramp_alias	dst=x5, sym=__sdei_asm_exit_trampoline, tmp=x3
+1:	tramp_alias	dst=x5, sym=__sdei_asm_exit_trampoline, tmp=x3
 	br	x5
 #endif
 SYM_CODE_END(__sdei_asm_handler)
diff --git a/arch/arm64/kernel/sdei.c b/arch/arm64/kernel/sdei.c
index 830be01af32d..be7f6ea49956 100644
--- a/arch/arm64/kernel/sdei.c
+++ b/arch/arm64/kernel/sdei.c
@@ -20,8 +20,6 @@
 #include <asm/sysreg.h>
 #include <asm/vmap_stack.h>
 
-unsigned long sdei_exit_mode;
-
 /*
  * VMAP'd stacks checking for stack overflow on exception using sp as a scratch
  * register, meaning SDEI has to switch to its own stack. We need two stacks as
@@ -162,7 +160,7 @@ static int init_sdei_scs(void)
 	return err;
 }
 
-unsigned long sdei_arch_get_entry_point(int conduit)
+unsigned long sdei_arch_get_entry_point(void)
 {
 	/*
 	 * SDEI works between adjacent exception levels. If we booted at EL1 we
@@ -181,8 +179,6 @@ unsigned long sdei_arch_get_entry_point(int conduit)
 	if (init_sdei_scs())
 		goto out_err_free_stacks;
 
-	sdei_exit_mode = (conduit == SMCCC_CONDUIT_HVC) ? SDEI_EXIT_HVC : SDEI_EXIT_SMC;
-
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 	if (arm64_kernel_unmapped_at_el0()) {
 		unsigned long offset;
@@ -262,3 +258,27 @@ unsigned long __kprobes do_sdei_event(struct pt_regs *regs,
 
 	return vbar + 0x480;
 }
+
+/*
+ * Patch in the sdei conduit instruction.
+ */
+void __init sdei_patch_conduit(struct alt_instr *alt, __le32 *origptr,
+			       __le32 *updptr, int nr_inst)
+{
+	u32 insn;
+
+	BUG_ON(nr_inst != 1); /* NOP -> HVC/SMC */
+
+	switch (sdei_get_conduit()) {
+	case SMCCC_CONDUIT_HVC:
+		insn = aarch64_insn_get_hvc_value();
+		break;
+	case SMCCC_CONDUIT_SMC:
+		insn = aarch64_insn_get_smc_value();
+		break;
+	default:
+		return;
+	}
+
+	*updptr = cpu_to_le32(insn);
+}
diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index b8ec7b3ac9cb..6286c4c59074 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/acpi.h>
+#include <linux/arm_sdei.h>
 #include <linux/export.h>
 #include <linux/kernel.h>
 #include <linux/stddef.h>
@@ -365,6 +366,8 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
 	else
 		psci_acpi_init();
 
+	sdei_conduit_init();
+
 	init_bootcpu_ops();
 	smp_init_cpus();
 	smp_build_mpidr_hash();
diff --git a/drivers/firmware/arm_sdei.c b/drivers/firmware/arm_sdei.c
index 1e1a51510e83..0dbb88bcc9a2 100644
--- a/drivers/firmware/arm_sdei.c
+++ b/drivers/firmware/arm_sdei.c
@@ -919,37 +919,12 @@ int sdei_unregister_ghes(struct ghes *ghes)
 	return err;
 }
 
-static int sdei_get_conduit(struct platform_device *pdev)
+enum arm_smccc_conduit sdei_get_conduit(void)
 {
-	const char *method;
-	struct device_node *np = pdev->dev.of_node;
-
-	sdei_firmware_call = NULL;
-	if (np) {
-		if (of_property_read_string(np, "method", &method)) {
-			pr_warn("missing \"method\" property\n");
-			return SMCCC_CONDUIT_NONE;
-		}
-
-		if (!strcmp("hvc", method)) {
-			sdei_firmware_call = &sdei_smccc_hvc;
-			return SMCCC_CONDUIT_HVC;
-		} else if (!strcmp("smc", method)) {
-			sdei_firmware_call = &sdei_smccc_smc;
-			return SMCCC_CONDUIT_SMC;
-		}
-
-		pr_warn("invalid \"method\" property: %s\n", method);
-	} else if (!acpi_disabled) {
-		if (acpi_psci_use_hvc()) {
-			sdei_firmware_call = &sdei_smccc_hvc;
-			return SMCCC_CONDUIT_HVC;
-		} else {
-			sdei_firmware_call = &sdei_smccc_smc;
-			return SMCCC_CONDUIT_SMC;
-		}
-	}
-
+	if (sdei_firmware_call == sdei_smccc_hvc)
+		return SMCCC_CONDUIT_HVC;
+	if (sdei_firmware_call == sdei_smccc_smc)
+		return SMCCC_CONDUIT_SMC;
 	return SMCCC_CONDUIT_NONE;
 }
 
@@ -957,9 +932,7 @@ static int sdei_probe(struct platform_device *pdev)
 {
 	int err;
 	u64 ver = 0;
-	int conduit;
 
-	conduit = sdei_get_conduit(pdev);
 	if (!sdei_firmware_call)
 		return 0;
 
@@ -984,7 +957,7 @@ static int sdei_probe(struct platform_device *pdev)
 	if (err)
 		return err;
 
-	sdei_entry_point = sdei_arch_get_entry_point(conduit);
+	sdei_entry_point = sdei_arch_get_entry_point();
 	if (!sdei_entry_point) {
 		/* Not supported due to hardware or boot configuration */
 		sdei_mark_interface_broken();
@@ -1059,6 +1032,38 @@ static bool __init sdei_present_acpi(void)
 	return true;
 }
 
+void __init sdei_conduit_init(void)
+{
+	const char *method;
+	struct device_node *np;
+
+	if (acpi_disabled) {
+		np = of_find_matching_node_and_match(NULL, sdei_of_match, NULL);
+		if (!np || !of_device_is_available(np))
+			return;
+
+		if (of_property_read_string(np, "method", &method)) {
+			pr_warn("missing \"method\" property\n");
+			return;
+		}
+
+		if (!strcmp("hvc", method))
+			sdei_firmware_call = &sdei_smccc_hvc;
+		else if (!strcmp("smc", method))
+			sdei_firmware_call = &sdei_smccc_smc;
+		else
+			pr_warn("invalid \"method\" property: %s\n", method);
+	} else {
+		if (!sdei_present_acpi())
+			return;
+
+		if (acpi_psci_use_hvc())
+			sdei_firmware_call = &sdei_smccc_hvc;
+		else
+			sdei_firmware_call = &sdei_smccc_smc;
+	}
+}
+
 void __init sdei_init(void)
 {
 	struct platform_device *pdev;
diff --git a/include/linux/arm_sdei.h b/include/linux/arm_sdei.h
index 14dc461b0e82..de9aafd87c48 100644
--- a/include/linux/arm_sdei.h
+++ b/include/linux/arm_sdei.h
@@ -13,7 +13,7 @@
 
 /* Arch code should override this to set the entry point from firmware... */
 #ifndef sdei_arch_get_entry_point
-#define sdei_arch_get_entry_point(conduit)	(0)
+#define sdei_arch_get_entry_point()	(0)
 #endif
 
 /*
@@ -22,6 +22,8 @@
  */
 typedef int (sdei_event_callback)(u32 event, struct pt_regs *regs, void *arg);
 
+enum arm_smccc_conduit sdei_get_conduit(void);
+
 /*
  * Register your callback to claim an event. The event must be described
  * by firmware.
@@ -47,10 +49,12 @@ int sdei_unregister_ghes(struct ghes *ghes);
 int sdei_mask_local_cpu(void);
 int sdei_unmask_local_cpu(void);
 void __init sdei_init(void);
+void __init sdei_conduit_init(void);
 #else
 static inline int sdei_mask_local_cpu(void) { return 0; }
 static inline int sdei_unmask_local_cpu(void) { return 0; }
 static inline void sdei_init(void) { }
+static inline void sdei_conduit_init(void) { }
 #endif /* CONFIG_ARM_SDE_INTERFACE */
 
 
-- 
2.39.2

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