linux-kernel - Re: [PATCH] x86/MCE: Remove MCP

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Date:   Wed, 18 Jan 2017 21:34:13 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "Luck, Tony" <tony.luck@...el.com>,
        linux-edac <linux-edac@...r.kernel.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/MCE: Remove MCP_TIMESTAMP

On Wed, Nov 09, 2016 at 07:06:04PM +0100, Borislav Petkov wrote:
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 4ca00474804b..3fbe80066b4e 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -706,6 +706,17 @@ bool machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
>  
>  	mce_gather_info(&m, NULL);
>  
> +	/*
> +	 * m.tsc was set in mce_setup(). Clear it if not requested.
> +	 *
> +	 * FIXME: Propagate @flags to mce_gather_info/mce_setup() to avoid
> +	 *	  that dance.
> +	 */

Lemme try to address that FIXME. So it doesn't look particularly easy to
do without touching/changing a bunch of places. That's why I'm trying
tricks first.

For example, the mce-apei.c case I'm addressing by setting ->tsc only
for errors of panic severity. The idea there is, that, panic errors will
have raised an #MC and not polled.

And then instead of propagating a flag to mce_setup(), it seems
easier/less code to set ->tsc depending on the call sites, i.e.,
are we polling or are we preparing an MCE record in an exception
handler/thresholding interrupt.

I'll run it tomorrow.

---
diff --git a/arch/x86/kernel/cpu/mcheck/mce-apei.c b/arch/x86/kernel/cpu/mcheck/mce-apei.c
index 83f1a98d37db..2eee85379689 100644
--- a/arch/x86/kernel/cpu/mcheck/mce-apei.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-apei.c
@@ -52,8 +52,11 @@ void apei_mce_report_mem_error(int severity, struct cper_sec_mem_err *mem_err)
 
 	if (severity >= GHES_SEV_RECOVERABLE)
 		m.status |= MCI_STATUS_UC;
-	if (severity >= GHES_SEV_PANIC)
+
+	if (severity >= GHES_SEV_PANIC) {
 		m.status |= MCI_STATUS_PCC;
+		m.tsc = rdtsc();
+	}
 
 	m.addr = mem_err->physical_addr;
 	mce_log(&m);
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 6eef6fde0f02..ca15a7e1f97d 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -128,7 +128,6 @@ void mce_setup(struct mce *m)
 {
 	memset(m, 0, sizeof(struct mce));
 	m->cpu = m->extcpu = smp_processor_id();
-	m->tsc = rdtsc();
 	/* We hope get_seconds stays lockless */
 	m->time = get_seconds();
 	m->cpuvendor = boot_cpu_data.x86_vendor;
@@ -710,14 +709,8 @@ bool machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
 
 	mce_gather_info(&m, NULL);
 
-	/*
-	 * m.tsc was set in mce_setup(). Clear it if not requested.
-	 *
-	 * FIXME: Propagate @flags to mce_gather_info/mce_setup() to avoid
-	 *	  that dance.
-	 */
-	if (!(flags & MCP_TIMESTAMP))
-		m.tsc = 0;
+	if (flags & MCP_TIMESTAMP)
+		m.tsc = rdtsc();
 
 	for (i = 0; i < mca_cfg.banks; i++) {
 		if (!mce_banks[i].ctl || !test_bit(i, *b))
@@ -1156,6 +1149,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 		goto out;
 
 	mce_gather_info(&m, regs);
+	m.tsc = rdtsc();
 
 	final = this_cpu_ptr(&mces_seen);
 	*final = m;
diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c b/arch/x86/kernel/cpu/mcheck/mce_amd.c
index 776379e4a39c..9e5427df3243 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
@@ -778,7 +778,8 @@ __log_error(unsigned int bank, bool deferred_err, bool threshold_err, u64 misc)
 	mce_setup(&m);
 
 	m.status = status;
-	m.bank = bank;
+	m.bank   = bank;
+	m.tsc	 = rdtsc();
 
 	if (threshold_err)
 		m.misc = misc;

-- 
Regards/Gruss,
    Boris.

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