On Fri, Sep 25, 2020 at 12:49 PM Catalin Marinas
[off-list ref] wrote:

quoted

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index a3bd189602df..d110f382dacf 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c

@@ -33,6 +33,7 @@
 #include <asm/debug-monitors.h>
 #include <asm/esr.h>
 #include <asm/kprobes.h>
+#include <asm/mte.h>
 #include <asm/processor.h>
 #include <asm/sysreg.h>
 #include <asm/system_misc.h>

@@ -294,6 +295,11 @@ static void die_kernel_fault(const char *msg, unsigned long addr,
      do_exit(SIGKILL);
 }

+static void report_tag_fault(unsigned long addr, unsigned int esr,
+                          struct pt_regs *regs)
+{
+}

Do we need to introduce report_tag_fault() in this patch? It's fine but
add a note in the commit log that it will be populated in a subsequent
patch.

I did, see the last line of the commit description.

quoted

+
 static void __do_kernel_fault(unsigned long addr, unsigned int esr,
                            struct pt_regs *regs)
 {

@@ -641,10 +647,40 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
      return 0;
 }

+static void do_tag_recovery(unsigned long addr, unsigned int esr,
+                        struct pt_regs *regs)
+{
+     static bool reported = false;
+
+     if (!READ_ONCE(reported)) {
+             report_tag_fault(addr, esr, regs);
+             WRITE_ONCE(reported, true);
+     }

I don't mind the READ_ONCE/WRITE_ONCE here but not sure what they help
with.

The fault can happen on multiple cores at the same time, right? In
that case without READ/WRITE_ONCE() we'll have a data-race here.

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