Re: [PATCH v5 2/2] x86/mce: Add support for Extended Physical Address MCA changes

Borislav Petkov
2022-04-13T14:54:11Z

On Wed, Apr 13, 2022 at 02:10:30PM +0000, Yazen Ghannam wrote:
> This function gets called from __mcheck_cpu_init_early() so that the info is
> available before the MCA banks are polled in __mcheck_cpu_init_generic().

Would that work?

I've moved first bank polling into __mcheck_cpu_init_clear_banks()
because, well, this function is clearing the banks so it might as well
poll them first. First bank polling in a init_generic function doesn't
make too much sense anyway.

And __mcheck_cpu_check_banks() functionality is moved into
__mcheck_cpu_init_clear_banks() because, well, silly.

On a quick scan, I don't see problems with such move but the devil is in
the detail.

Hmm?

---

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 99e3ff9607a3..345e068215c4 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1732,21 +1732,8 @@ static void __mcheck_cpu_cap_init(void)

static void __mcheck_cpu_init_generic(void)
{
- enum mcp_flags m_fl = 0;
- mce_banks_t all_banks;
u64 cap;

- if (!mca_cfg.bootlog)
- m_fl = MCP_DONTLOG;
-
- /*
- * 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 | MCP_QUEUE_LOG | m_fl, &all_banks);
-
cr4_set_bits(X86_CR4_MCE);

rdmsrl(MSR_IA32_MCG_CAP, cap);
@@ -1757,33 +1744,21 @@ static void __mcheck_cpu_init_generic(void)
static void __mcheck_cpu_init_clear_banks(void)
{
struct mce_bank *mce_banks = this_cpu_ptr(mce_banks_array);
+ enum mcp_flags m_fl = 0;
+ mce_banks_t all_banks;
+ u64 msrval;
int i;

- for (i = 0; i < this_cpu_read(mce_num_banks); i++) {
- struct mce_bank *b = &mce_banks[i];
-
- if (!b->init)
- continue;
- wrmsrl(mca_msr_reg(i, MCA_CTL), b->ctl);
- wrmsrl(mca_msr_reg(i, MCA_STATUS), 0);
- }
-}
+ if (!mca_cfg.bootlog)
+ m_fl = MCP_DONTLOG;

-/*
- * Do a final check to see if there are any unused/RAZ banks.
- *
- * This must be done after the banks have been initialized and any quirks have
- * been applied.
- *
- * Do not call this from any user-initiated flows, e.g. CPU hotplug or sysfs.
- * Otherwise, a user who disables a bank will not be able to re-enable it
- * without a system reboot.
- */
-static void __mcheck_cpu_check_banks(void)
-{
- struct mce_bank *mce_banks = this_cpu_ptr(mce_banks_array);
- u64 msrval;
- int i;
+ /*
+ * 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 | MCP_QUEUE_LOG | m_fl, &all_banks);

for (i = 0; i < this_cpu_read(mce_num_banks); i++) {
struct mce_bank *b = &mce_banks[i];
@@ -1791,6 +1766,9 @@ static void __mcheck_cpu_check_banks(void)
if (!b->init)
continue;

+ wrmsrl(mca_msr_reg(i, MCA_CTL), b->ctl);
+ wrmsrl(mca_msr_reg(i, MCA_STATUS), 0);
+
rdmsrl(mca_msr_reg(i, MCA_CTL), msrval);
b->init = !!msrval;
}
@@ -2159,7 +2137,6 @@ void mcheck_cpu_init(struct cpuinfo_x86 *c)
__mcheck_cpu_init_generic();
__mcheck_cpu_init_vendor(c);
__mcheck_cpu_init_clear_banks();
- __mcheck_cpu_check_banks();
__mcheck_cpu_setup_timer();
}

--
Regards/Gruss,
Boris.