powerpc/64s: Add workaround for P9 vector CI load issue

POWER9 DD2.1 and earlier has an issue where some cache inhibited
vector load will return bad data. The workaround is two part, one
firmware/microcode part triggers HMI interrupts when hitting such
loads, the other part is this patch which then emulates the
instructions in Linux.

The affected instructions are limited to lxvd2x, lxvw4x, lxvb16x and
lxvh8x.

When an instruction triggers the HMI, all threads in the core will be
sent to the HMI handler, not just the one running the vector load.

In general, these spurious HMIs are detected by the emulation code and
we just return back to the running process. Unfortunately, if a
spurious interrupt occurs on a vector load that's to normal memory we
have no way to detect that it's spurious (unless we walk the page
tables, which is very expensive). In this case we emulate the load but
we need do so using a vector load itself to ensure 128bit atomicity is
preserved.

Some additional debugfs emulated instruction counters are added also.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[mpe: Switch CONFIG_PPC_BOOK3S_64 to CONFIG_VSX to unbreak the build]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 29 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
index 9b2ea7e71c06d..f588951b171d0 100644
--- a/arch/powerpc/kernel/mce.c
+++ b/arch/powerpc/kernel/mce.c
@@ -470,6 +470,34 @@ long hmi_exception_realmode(struct pt_regs *regs)
 {
 	__this_cpu_inc(irq_stat.hmi_exceptions);
 
+#ifdef CONFIG_PPC_BOOK3S_64
+	/* Workaround for P9 vector CI loads (see p9_hmi_special_emu) */
+	if (pvr_version_is(PVR_POWER9)) {
+		unsigned long hmer = mfspr(SPRN_HMER);
+
+		/* Do we have the debug bit set */
+		if (hmer & PPC_BIT(17)) {
+			hmer &= ~PPC_BIT(17);
+			mtspr(SPRN_HMER, hmer);
+
+			/*
+			 * Now to avoid problems with soft-disable we
+			 * only do the emulation if we are coming from
+			 * user space
+			 */
+			if (user_mode(regs))
+				local_paca->hmi_p9_special_emu = 1;
+
+			/*
+			 * Don't bother going to OPAL if that's the
+			 * only relevant bit.
+			 */
+			if (!(hmer & mfspr(SPRN_HMEER)))
+				return local_paca->hmi_p9_special_emu;
+		}
+	}
+#endif /* CONFIG_PPC_BOOK3S_64 */
+
 	wait_for_subcore_guest_exit();
 
 	if (ppc_md.hmi_exception_early)
@@ -477,5 +505,5 @@ long hmi_exception_realmode(struct pt_regs *regs)
 
 	wait_for_tb_resync();
 
-	return 0;
+	return 1;
 }