x86/mce: Defer processing of early errors

[ Upstream commit 3bff147b187d5dfccfca1ee231b0761a89f1eff5 ]

When a fatal machine check results in a system reset, Linux does not
clear the error(s) from machine check bank(s) - hardware preserves the
machine check banks across a warm reset.

During initialization of the kernel after the reboot, Linux reads, logs,
and clears all machine check banks.

But there is a problem. In:

  5de97c9f6d85 ("x86/mce: Factor out and deprecate the /dev/mcelog driver")

the call to mce_register_decode_chain() moved later in the boot
sequence. This means that /dev/mcelog doesn't see those early error
logs.

This was partially fixed by:

  cd9c57cad3fe ("x86/MCE: Dump MCE to dmesg if no consumers")

which made sure that the logs were not lost completely by printing
to the console. But parsing console logs is error prone. Users of
/dev/mcelog should expect to find any early errors logged to standard
places.

Add a new flag MCP_QUEUE_LOG to machine_check_poll() to be used in early
machine check initialization to indicate that any errors found should
just be queued to genpool. When mcheck_late_init() is called it will
call mce_schedule_work() to actually log and flush any errors queued in
the genpool.

 [ Based on an original patch, commit message by and completely
   productized by Tony Luck. ]

Fixes: 5de97c9f6d85 ("x86/mce: Factor out and deprecate the /dev/mcelog driver")
Reported-by: Sumanth Kamatala <skamatala@juniper.net>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210824003129.GA1642753@agluck-desk2.amr.corp.intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/include/asm/mce.h b/arch/x86/include/asm/mce.h
index ddfb3cad8dff2a447979774f56817c2802ce5b1d..2a8319fad0b75602555806bc9e929b5e0f996e2c 100644 (file)
--- a/arch/x86/include/asm/mce.h
+++ b/arch/x86/include/asm/mce.h
@@ -265,6 +265,7 @@ enum mcp_flags {
        MCP_TIMESTAMP   = BIT(0),       /* log time stamp */
        MCP_UC          = BIT(1),       /* log uncorrected errors */
        MCP_DONTLOG     = BIT(2),       /* only clear, don't log */
+       MCP_QUEUE_LOG   = BIT(3),       /* only queue to genpool */
 };
 bool machine_check_poll(enum mcp_flags flags, mce_banks_t *b);
 

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index bf7fe87a7e884d3006f20f76a113e8289618ebe9..01ff4014b7f67dfe280f08a79387ab93ede57c58 100644 (file)
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -817,7 +817,10 @@ log_it:
                if (mca_cfg.dont_log_ce && !mce_usable_address(&m))
                        goto clear_it;
 
-               mce_log(&m);
+               if (flags & MCP_QUEUE_LOG)
+                       mce_gen_pool_add(&m);
+               else
+                       mce_log(&m);
 
 clear_it:
                /*
@@ -1630,10 +1633,12 @@ static void __mcheck_cpu_init_generic(void)
                m_fl = MCP_DONTLOG;
 
        /*
-        * Log the machine checks left over from the previous reset.
+        * Log the machine checks left over from the previous reset. Log them
+        * only, do not start processing them. That will happen in mcheck_late_init()
+        * when all consumers have been registered on the notifier chain.
         */
        bitmap_fill(all_banks, MAX_NR_BANKS);
-       machine_check_poll(MCP_UC | m_fl, &all_banks);
+       machine_check_poll(MCP_UC | MCP_QUEUE_LOG | m_fl, &all_banks);
 
        cr4_set_bits(X86_CR4_MCE);