Re: [PATCH] x86/MCE: Remove MCP_TIMESTAMP

[Borislav Petkov <bp@alien8.de>]

On Wed, Jan 18, 2017 at 09:34:13PM +0100, Borislav Petkov wrote:
> I'll run it tomorrow.

Ok, here it is, it looks ok while testing in a guest and injecting MCEs.

---
From: Borislav Petkov <bp@suse.de>
Date: Wed, 18 Jan 2017 21:34:41 +0100
Subject: [PATCH] x86/MCE: Flip the TSC-adding logic

Add the TSC value to the MCE record only when the MCE being logged is
precise, i.e., it is logged as an exception or an MCE-related interrupt.

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.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kernel/cpu/mcheck/mce-apei.c |  5 ++++-
 arch/x86/kernel/cpu/mcheck/mce.c      | 12 +++---------
 arch/x86/kernel/cpu/mcheck/mce_amd.c  |  3 ++-
 3 files changed, 9 insertions(+), 11 deletions(-)

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;
-- 
2.11.0

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.