[v2,6/6] x86/MCE: Treat MCE bank as initialized if control bits set in hardware

[Yazen Ghannam <yazen.ghannam@amd.com>]

From: Yazen Ghannam <yazen.ghannam@amd.com>

The OS is expected to write all bits to MCA_CTL for each bank. However,
some banks may be unused in which case the registers for such banks are
Read-as-Zero/Writes-Ignored. Also, the OS may not write any control bits
because of quirks, etc.

A bank can be considered uninitialized if the MCA_CTL register returns
zero. This is because either the OS did not write anything or because
the hardware is enforcing RAZ/WI for the bank.

Set a bank's init value based on if the control bits are set or not in
hardware.

Return an error code in the sysfs interface for uninitialized banks.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
---
Link:
https://lkml.kernel.org/r/20190408141205.12376-3-Yazen.Ghannam@amd.com

v1->v2:
* New in v2.
* Based on discussion from v1 patch 2.

 arch/x86/kernel/cpu/mce/core.c | 9 +++++++++
 1 file changed, 9 insertions(+)

-- 
2.17.1

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 71662133c70c..dcf5c6d72811 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1572,6 +1572,9 @@ static void __mcheck_cpu_init_clear_banks(void)
 
 		/* Save bits set in hardware. */
 		rdmsrl(msr_ops.ctl(i), b->ctl);
+
+		/* Bank is initialized if bits are set in hardware. */
+		b->init = !!b->ctl;
 	}
 }
 
@@ -2086,6 +2089,9 @@ static ssize_t show_bank(struct device *s, struct device_attribute *attr,
 
 	b = &per_cpu(mce_banks, s->id)[bank];
 
+	if (!b->init)
+		return -ENODEV;
+
 	return sprintf(buf, "%llx\n", b->ctl);
 }
 
@@ -2104,6 +2110,9 @@ static ssize_t set_bank(struct device *s, struct device_attribute *attr,
 
 	b = &per_cpu(mce_banks, s->id)[bank];
 
+	if (!b->init)
+		return -ENODEV;
+
 	b->ctl = new;
 	mce_restart();