powerpc/icswx: Simple ACOP fault handler

This patch adds a fault handler that responds to illegal Coprocessor
types.  Currently all CTs are treated and illegal.  There are two ways
to report the fault back to the application.  If the application used
the record form ("icswx.") then the architected "reject" is emulated.
If the application did not used the record form ("icswx") then it is
selectable by config whether the failure is silent (as architected) or
a SIGILL is generated.

In all cases pr_warn() is used to log the bad CT.

Signed-off-by: Jimi Xenidis <jimix@pobox.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 113 insertions, 0 deletions

diff --git a/arch/powerpc/mm/icswx.c b/arch/powerpc/mm/icswx.c
index a98850fd7777..5d9a59eaad93 100644
--- a/arch/powerpc/mm/icswx.c
+++ b/arch/powerpc/mm/icswx.c
@@ -17,6 +17,8 @@
 #include <linux/mm.h>
 #include <linux/spinlock.h>
 #include <linux/module.h>
+#include <linux/uaccess.h>
+
 #include "icswx.h"
 
 /*
@@ -158,3 +160,114 @@ void drop_cop(unsigned long acop, struct mm_struct *mm)
 	spin_unlock(&mm->page_table_lock);
 }
 EXPORT_SYMBOL_GPL(drop_cop);
+
+static int acop_use_cop(int ct)
+{
+	/* todo */
+	return -1;
+}
+
+/*
+ * Get the instruction word at the NIP
+ */
+static u32 acop_get_inst(struct pt_regs *regs)
+{
+	u32 inst;
+	u32 __user *p;
+
+	p = (u32 __user *)regs->nip;
+	if (!access_ok(VERIFY_READ, p, sizeof(*p)))
+		return 0;
+
+	if (__get_user(inst, p))
+		return 0;
+
+	return inst;
+}
+
+/**
+ * @regs: regsiters at time of interrupt
+ * @address: storage address
+ * @error_code: Fault code, usually the DSISR or ESR depending on
+ *		processor type
+ *
+ * Return 0 if we are able to resolve the data storage fault that
+ * results from a CT miss in the ACOP register.
+ */
+int acop_handle_fault(struct pt_regs *regs, unsigned long address,
+		      unsigned long error_code)
+{
+	int ct;
+	u32 inst = 0;
+
+	if (!cpu_has_feature(CPU_FTR_ICSWX)) {
+		pr_info("No coprocessors available");
+		_exception(SIGILL, regs, ILL_ILLOPN, address);
+	}
+
+	if (!user_mode(regs)) {
+		/* this could happen if the HV denies the
+		 * kernel access, for now we just die */
+		die("ICSWX from kernel failed", regs, SIGSEGV);
+	}
+
+	/* Some implementations leave us a hint for the CT */
+	ct = ICSWX_GET_CT_HINT(error_code);
+	if (ct < 0) {
+		/* we have to peek at the instruction word to figure out CT */
+		u32 ccw;
+		u32 rs;
+
+		inst = acop_get_inst(regs);
+		if (inst == 0)
+			return -1;
+
+		rs = (inst >> (31 - 10)) & 0x1f;
+		ccw = regs->gpr[rs];
+		ct = (ccw >> 16) & 0x3f;
+	}
+
+	if (!acop_use_cop(ct))
+		return 0;
+
+	/* at this point the CT is unknown to the system */
+	pr_warn("%s[%d]: Coprocessor %d is unavailable",
+		current->comm, current->pid, ct);
+
+	/* get inst if we don't already have it */
+	if (inst == 0) {
+		inst = acop_get_inst(regs);
+		if (inst == 0)
+			return -1;
+	}
+
+	/* Check if the instruction is the "record form" */
+	if (inst & 1) {
+		/*
+		 * the instruction is "record" form so we can reject
+		 * using CR0
+		 */
+		regs->ccr &= ~(0xful << 28);
+		regs->ccr |= ICSWX_RC_NOT_FOUND << 28;
+
+		/* Move on to the next instruction */
+		regs->nip += 4;
+	} else {
+		/*
+		 * There is no architected mechanism to report a bad
+		 * CT so we could either SIGILL or report nothing.
+		 * Since the non-record version should only bu used
+		 * for "hints" or "don't care" we should probably do
+		 * nothing.  However, I could see how some people
+		 * might want an SIGILL so it here if you want it.
+		 */
+#ifdef CONFIG_PPC_ICSWX_USE_SIGILL
+		_exception(SIGILL, regs, ILL_ILLOPN, address);
+#else
+		regs->nip += 4;
+#endif
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(acop_handle_fault);