linux-kernel - [v5 5/6] powerpc/mce: Handle UE event for memcpy

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Date:   Tue,  9 Jul 2019 17:45:23 +0530
From:   Santosh Sivaraj <santosh@...six.org>
To:     linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-kernel@...r.kernel.org
Cc:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Mahesh Salgaonkar <mahesh@...ux.ibm.com>,
        Reza Arbab <arbab@...ux.ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        Chandan Rajendra <chandan@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        christophe leroy <christophe.leroy@....fr>
Subject: [v5 5/6] powerpc/mce: Handle UE event for memcpy_mcsafe

If we take a UE on one of the instructions with a fixup entry, set nip
to continue execution at the fixup entry. Stop processing the event
further or print it.

Based-on-patch-by: Reza Arbab <arbab@...ux.ibm.com>
Cc: Reza Arbab <arbab@...ux.ibm.com>
Cc: Mahesh Salgaonkar <mahesh@...ux.ibm.com>
Signed-off-by: Santosh Sivaraj <santosh@...six.org>
---
 arch/powerpc/include/asm/mce.h  |  4 +++-
 arch/powerpc/kernel/mce.c       | 12 +++++++++++-
 arch/powerpc/kernel/mce_power.c | 15 +++++++++++++--
 3 files changed, 27 insertions(+), 4 deletions(-)

Nick, I didn't add has_fixup_handler in mce_event structure; if we do so we wil
have to access the mce_event from ue_handler code also. That is because Mahesh
did not want mce_event to be accessed outside of save_mce_event, get_mce_event
and remove_mce_event; that is why I added ignore_event in mce_err also.

I have added the comment you mentioned in your reply.

diff --git a/arch/powerpc/include/asm/mce.h b/arch/powerpc/include/asm/mce.h
index 94888a7025b3..f74257eb013b 100644
--- a/arch/powerpc/include/asm/mce.h
+++ b/arch/powerpc/include/asm/mce.h
@@ -122,7 +122,8 @@ struct machine_check_event {
 			enum MCE_UeErrorType ue_error_type:8;
 			u8		effective_address_provided;
 			u8		physical_address_provided;
-			u8		reserved_1[5];
+			u8		ignore_event;
+			u8		reserved_1[4];
 			u64		effective_address;
 			u64		physical_address;
 			u8		reserved_2[8];
@@ -193,6 +194,7 @@ struct mce_error_info {
 	enum MCE_Initiator	initiator:8;
 	enum MCE_ErrorClass	error_class:8;
 	bool			sync_error;
+	bool			ignore_event;
 };
 
 #define MAX_MC_EVT	100
diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
index e78c4f18ea0a..092e6bbc603f 100644
--- a/arch/powerpc/kernel/mce.c
+++ b/arch/powerpc/kernel/mce.c
@@ -144,7 +144,9 @@ void save_mce_event(struct pt_regs *regs, long handled,
 		if (phys_addr != ULONG_MAX) {
 			mce->u.ue_error.physical_address_provided = true;
 			mce->u.ue_error.physical_address = phys_addr;
-			machine_check_ue_event(mce);
+			mce->u.ue_error.ignore_event = mce_err->ignore_event;
+			if (!mce->u.ue_error.ignore_event)
+				machine_check_ue_event(mce);
 		}
 	}
 	return;
@@ -230,6 +232,14 @@ void machine_check_queue_event(void)
 	if (!get_mce_event(&evt, MCE_EVENT_RELEASE))
 		return;
 
+	/*
+	 * Don't report this machine check because the caller has a asked us
+	 * to ignore the event, it has a fixup handler which will do the
+	 * appropriate error handling and reporting.
+	 */
+	if (evt.error_type == MCE_ERROR_TYPE_UE && evt.u.ue_error.ignore_event)
+		return;
+
 	index = __this_cpu_inc_return(mce_queue_count) - 1;
 	/* If queue is full, just return for now. */
 	if (index >= MAX_MC_EVT) {
diff --git a/arch/powerpc/kernel/mce_power.c b/arch/powerpc/kernel/mce_power.c
index 04666c0b40a8..582a22b1acfb 100644
--- a/arch/powerpc/kernel/mce_power.c
+++ b/arch/powerpc/kernel/mce_power.c
@@ -11,6 +11,7 @@
 
 #include <linux/types.h>
 #include <linux/ptrace.h>
+#include <linux/extable.h>
 #include <asm/mmu.h>
 #include <asm/mce.h>
 #include <asm/machdep.h>
@@ -18,6 +19,7 @@
 #include <asm/pte-walk.h>
 #include <asm/sstep.h>
 #include <asm/exception-64s.h>
+#include <asm/extable.h>
 
 /*
  * Convert an address related to an mm to a PFN. NOTE: we are in real
@@ -565,9 +567,18 @@ static int mce_handle_derror(struct pt_regs *regs,
 	return 0;
 }
 
-static long mce_handle_ue_error(struct pt_regs *regs)
+static long mce_handle_ue_error(struct pt_regs *regs,
+				struct mce_error_info *mce_err)
 {
 	long handled = 0;
+	const struct exception_table_entry *entry;
+
+	entry = search_kernel_exception_table(regs->nip);
+	if (entry) {
+		mce_err->ignore_event = true;
+		regs->nip = extable_fixup(entry);
+		return 1;
+	}
 
 	/*
 	 * On specific SCOM read via MMIO we may get a machine check
@@ -600,7 +611,7 @@ static long mce_handle_error(struct pt_regs *regs,
 				&phys_addr);
 
 	if (!handled && mce_err.error_type == MCE_ERROR_TYPE_UE)
-		handled = mce_handle_ue_error(regs);
+		handled = mce_handle_ue_error(regs, &mce_err);
 
 	save_mce_event(regs, handled, &mce_err, regs->nip, addr, phys_addr);
 
-- 
2.20.1