arm64: mops: handle MOPS exceptions

The memory copy/set instructions added as part of FEAT_MOPS can take an
exception (e.g. page fault) part-way through their execution and resume
execution afterwards.

If however the task is re-scheduled and execution resumes on a different
CPU, then the CPU may take a new type of exception to indicate this.
This is because the architecture allows two options (Option A and Option
B) to implement the instructions and a heterogeneous system can have
different implementations between CPUs.

In this case the OS has to reset the registers and restart execution
from the prologue instruction. The algorithm for doing this is provided
as part of the Arm ARM.

Add an exception handler for the new exception and wire it up for
userspace tasks.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
Link: https://lore.kernel.org/r/20230509142235.3284028-8-kristina.martsenko@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: kristina-martsenko

arch/arm64/include/asm/esr.h

@@ -47,7 +47,7 @@
 #define ESR_ELx_EC_DABT_LOW	(0x24)
 #define ESR_ELx_EC_DABT_CUR	(0x25)
 #define ESR_ELx_EC_SP_ALIGN	(0x26)
-/* Unallocated EC: 0x27 */
+#define ESR_ELx_EC_MOPS		(0x27)
 #define ESR_ELx_EC_FP_EXC32	(0x28)
 /* Unallocated EC: 0x29 - 0x2B */
 #define ESR_ELx_EC_FP_EXC64	(0x2C)
@@ -356,6 +356,15 @@
 #define ESR_ELx_SME_ISS_ZA_DISABLED	3
 #define ESR_ELx_SME_ISS_ZT_DISABLED	4
 
+/* ISS field definitions for MOPS exceptions */
+#define ESR_ELx_MOPS_ISS_MEM_INST	(UL(1) << 24)
+#define ESR_ELx_MOPS_ISS_FROM_EPILOGUE	(UL(1) << 18)
+#define ESR_ELx_MOPS_ISS_WRONG_OPTION	(UL(1) << 17)
+#define ESR_ELx_MOPS_ISS_OPTION_A	(UL(1) << 16)
+#define ESR_ELx_MOPS_ISS_DESTREG(esr)	(((esr) & (UL(0x1f) << 10)) >> 10)
+#define ESR_ELx_MOPS_ISS_SRCREG(esr)	(((esr) & (UL(0x1f) << 5)) >> 5)
+#define ESR_ELx_MOPS_ISS_SIZEREG(esr)	(((esr) & (UL(0x1f) << 0)) >> 0)
+
 #ifndef __ASSEMBLY__
 #include <asm/types.h>
 

arch/arm64/include/asm/exception.h

@@ -77,6 +77,7 @@ void do_el0_svc(struct pt_regs *regs);
 void do_el0_svc_compat(struct pt_regs *regs);
 void do_el0_fpac(struct pt_regs *regs, unsigned long esr);
 void do_el1_fpac(struct pt_regs *regs, unsigned long esr);
+void do_el0_mops(struct pt_regs *regs, unsigned long esr);
 void do_serror(struct pt_regs *regs, unsigned long esr);
 void do_notify_resume(struct pt_regs *regs, unsigned long thread_flags);
 

arch/arm64/kernel/entry-common.c

@@ -611,6 +611,14 @@ static void noinstr el0_bti(struct pt_regs *regs)
 	exit_to_user_mode(regs);
 }
 
+static void noinstr el0_mops(struct pt_regs *regs, unsigned long esr)
+{
+	enter_from_user_mode(regs);
+	local_daif_restore(DAIF_PROCCTX);
+	do_el0_mops(regs, esr);
+	exit_to_user_mode(regs);
+}
+
 static void noinstr el0_inv(struct pt_regs *regs, unsigned long esr)
 {
 	enter_from_user_mode(regs);
@@ -688,6 +696,9 @@ asmlinkage void noinstr el0t_64_sync_handler(struct pt_regs *regs)
 	case ESR_ELx_EC_BTI:
 		el0_bti(regs);
 		break;
+	case ESR_ELx_EC_MOPS:
+		el0_mops(regs, esr);
+		break;
 	case ESR_ELx_EC_BREAKPT_LOW:
 	case ESR_ELx_EC_SOFTSTP_LOW:
 	case ESR_ELx_EC_WATCHPT_LOW:

arch/arm64/kernel/traps.c

@@ -514,6 +514,57 @@ void do_el1_fpac(struct pt_regs *regs, unsigned long esr)
 	die("Oops - FPAC", regs, esr);
 }
 
+void do_el0_mops(struct pt_regs *regs, unsigned long esr)
+{
+	bool wrong_option = esr & ESR_ELx_MOPS_ISS_WRONG_OPTION;
+	bool option_a = esr & ESR_ELx_MOPS_ISS_OPTION_A;
+	int dstreg = ESR_ELx_MOPS_ISS_DESTREG(esr);
+	int srcreg = ESR_ELx_MOPS_ISS_SRCREG(esr);
+	int sizereg = ESR_ELx_MOPS_ISS_SIZEREG(esr);
+	unsigned long dst, src, size;
+
+	dst = pt_regs_read_reg(regs, dstreg);
+	src = pt_regs_read_reg(regs, srcreg);
+	size = pt_regs_read_reg(regs, sizereg);
+
+	/*
+	 * Put the registers back in the original format suitable for a
+	 * prologue instruction, using the generic return routine from the
+	 * Arm ARM (DDI 0487I.a) rules CNTMJ and MWFQH.
+	 */
+	if (esr & ESR_ELx_MOPS_ISS_MEM_INST) {
+		/* SET* instruction */
+		if (option_a ^ wrong_option) {
+			/* Format is from Option A; forward set */
+			pt_regs_write_reg(regs, dstreg, dst + size);
+			pt_regs_write_reg(regs, sizereg, -size);
+		}
+	} else {
+		/* CPY* instruction */
+		if (!(option_a ^ wrong_option)) {
+			/* Format is from Option B */
+			if (regs->pstate & PSR_N_BIT) {
+				/* Backward copy */
+				pt_regs_write_reg(regs, dstreg, dst - size);
+				pt_regs_write_reg(regs, srcreg, src - size);
+			}
+		} else {
+			/* Format is from Option A */
+			if (size & BIT(63)) {
+				/* Forward copy */
+				pt_regs_write_reg(regs, dstreg, dst + size);
+				pt_regs_write_reg(regs, srcreg, src + size);
+				pt_regs_write_reg(regs, sizereg, -size);
+			}
+		}
+	}
+
+	if (esr & ESR_ELx_MOPS_ISS_FROM_EPILOGUE)
+		regs->pc -= 8;
+	else
+		regs->pc -= 4;
+}
+
 #define __user_cache_maint(insn, address, res)			\
 	if (address >= TASK_SIZE_MAX) {				\
 		res = -EFAULT;					\
@@ -824,6 +875,7 @@ static const char *esr_class_str[] = {
 	[ESR_ELx_EC_DABT_LOW]		= "DABT (lower EL)",
 	[ESR_ELx_EC_DABT_CUR]		= "DABT (current EL)",
 	[ESR_ELx_EC_SP_ALIGN]		= "SP Alignment",
+	[ESR_ELx_EC_MOPS]		= "MOPS",
 	[ESR_ELx_EC_FP_EXC32]		= "FP (AArch32)",
 	[ESR_ELx_EC_FP_EXC64]		= "FP (AArch64)",
 	[ESR_ELx_EC_SERROR]		= "SError",