Re: [PATCH v4 1/2] x86/mce: Check for writes ignored in MCA_STATUS register

Borislav Petkov
2022-04-06T17:56:14Z

On Mon, Feb 14, 2022 at 05:36:39PM -0600, Smita Koralahalli wrote:
> diff --git a/arch/x86/kernel/cpu/mce/inject.c b/arch/x86/kernel/cpu/mce/inject.c
> index 5fbd7ffb3233..43ba63b7dc73 100644
> --- a/arch/x86/kernel/cpu/mce/inject.c
> +++ b/arch/x86/kernel/cpu/mce/inject.c
> @@ -470,11 +470,36 @@ static void toggle_nb_mca_mst_cpu(u16 nid)
> __func__, PCI_FUNC(F3->devfn), NBCFG);
> }
>
> +struct mce_err_handler {
> + struct mce *mce;
> + int err;
> +};

Well, we already have a struct mce i_mce which serves as a sort-of
global container for injection data which gets dumped into the hardware
upon injection time.

Now you're adding another struct which contains additional info and are
adding a pointer to that i_mce.

But this is not a clean design - when you do stuff like that you need to
unify all those global-info-containing structs and make the code dealing
with them straight-forward . I.e., if you don't look at the big picture
of a design, it soon grows into an unwieldy mess which some poor sod
would need to clean up afterwards and that poor sod is in most cases the
maintainer.

So I went and did that ontop of your patch, this is one possible way to
do it but it.

Here it is, a combined diff ontop of tip:ras/core. Please split it into
patches: first patch converts to the new descriptor and then a second
one adds the MCA_STATUS checking bits.

There are a couple of other changes in there, if they're not clear, feel
free to ask.

Thx.

---
diff --git a/arch/x86/kernel/cpu/mce/inject.c b/arch/x86/kernel/cpu/mce/inject.c
index 43ba63b7dc73..0fd1eea2f754 100644
--- a/arch/x86/kernel/cpu/mce/inject.c
+++ b/arch/x86/kernel/cpu/mce/inject.c
@@ -33,10 +33,14 @@

#include "internal.h"

-/*
- * Collect all the MCi_XXX settings
- */
-static struct mce i_mce;
+static bool hw_injection_possible = true;
+
+/* Collect all the MCi_XXX settings */
+static struct inject_desc {
+ struct mce m;
+ int err;
+} inj_desc;
+
static struct dentry *dfs_inj;

#define MAX_FLAG_OPT_SIZE 4
@@ -110,9 +114,11 @@ static int inj_ipid_set(void *data, u64 val)

DEFINE_SIMPLE_ATTRIBUTE(ipid_fops, inj_ipid_get, inj_ipid_set, "%llx\n");

-static void setup_inj_struct(struct mce *m)
+static void setup_inj_struct(void)
{
- memset(m, 0, sizeof(struct mce));
+ struct mce *m = &inj_desc.m;
+
+ memset(&inj_desc, 0, sizeof(struct inject_desc));

m->cpuvendor = boot_cpu_data.x86_vendor;
m->time = ktime_get_real_seconds();
@@ -470,84 +476,78 @@ static void toggle_nb_mca_mst_cpu(u16 nid)
__func__, PCI_FUNC(F3->devfn), NBCFG);
}

-struct mce_err_handler {
- struct mce *mce;
- int err;
-};
-
-static struct mce_err_handler mce_err;
-
-static bool prepare_mca_status(struct mce *m)
+static bool prepare_mca_status(void)
{
- u32 status_reg = mca_msr_reg(m->bank, MCA_STATUS);
- u64 status_val = m->status;
+ u32 status_reg = mca_msr_reg(inj_desc.m.bank, MCA_STATUS);
+ u64 status_val = inj_desc.m.status;

wrmsrl(status_reg, status_val);
rdmsrl(status_reg, status_val);

- return status_val;
+ return status_val == inj_desc.m.status;
}

-static void prepare_msrs(void *info)
+static void prepare_msrs(void *unused)
{
- struct mce_err_handler *i_mce_err = ((struct mce_err_handler *)info);
- struct mce m = *i_mce_err->mce;
- u8 b = m.bank;
+ struct mce *m = &inj_desc.m;
+ u8 b = inj_desc.m.bank;

- if (!prepare_mca_status(&m)) {
+ if (!prepare_mca_status()) {
pr_err("Platform does not allow error injection, try using APEI EINJ instead.\n");
- i_mce_err->err = -EINVAL;
+ inj_desc.err = -EINVAL;
+ hw_injection_possible = false;
return;
}

- wrmsrl(MSR_IA32_MCG_STATUS, m.mcgstatus);
+ wrmsrl(MSR_IA32_MCG_STATUS, m->mcgstatus);

if (boot_cpu_has(X86_FEATURE_SMCA)) {
- if (m.inject_flags == DFR_INT_INJ) {
- wrmsrl(MSR_AMD64_SMCA_MCx_DESTAT(b), m.status);
- wrmsrl(MSR_AMD64_SMCA_MCx_DEADDR(b), m.addr);
+ if (m->inject_flags == DFR_INT_INJ) {
+ wrmsrl(MSR_AMD64_SMCA_MCx_DESTAT(b), m->status);
+ wrmsrl(MSR_AMD64_SMCA_MCx_DEADDR(b), m->addr);
} else {
- wrmsrl(MSR_AMD64_SMCA_MCx_STATUS(b), m.status);
- wrmsrl(MSR_AMD64_SMCA_MCx_ADDR(b), m.addr);
+ wrmsrl(MSR_AMD64_SMCA_MCx_STATUS(b), m->status);
+ wrmsrl(MSR_AMD64_SMCA_MCx_ADDR(b), m->addr);
}

- wrmsrl(MSR_AMD64_SMCA_MCx_MISC(b), m.misc);
- wrmsrl(MSR_AMD64_SMCA_MCx_SYND(b), m.synd);
+ wrmsrl(MSR_AMD64_SMCA_MCx_MISC(b), m->misc);
+ wrmsrl(MSR_AMD64_SMCA_MCx_SYND(b), m->synd);
} else {
- wrmsrl(MSR_IA32_MCx_STATUS(b), m.status);
- wrmsrl(MSR_IA32_MCx_ADDR(b), m.addr);
- wrmsrl(MSR_IA32_MCx_MISC(b), m.misc);
+ wrmsrl(MSR_IA32_MCx_STATUS(b), m->status);
+ wrmsrl(MSR_IA32_MCx_ADDR(b), m->addr);
+ wrmsrl(MSR_IA32_MCx_MISC(b), m->misc);
}
}

-static void do_inject(void)
+static int do_inject(void)
{
+ struct mce *m = &inj_desc.m;
+ unsigned int cpu = m->extcpu;
u64 mcg_status = 0;
- unsigned int cpu = i_mce.extcpu;
- u8 b = i_mce.bank;
+ u8 b = m->bank;

- mce_err.mce = &i_mce;
- mce_err.err = 0;
+ m->tsc = rdtsc_ordered();

- i_mce.tsc = rdtsc_ordered();
+ m->status |= MCI_STATUS_VAL;

- i_mce.status |= MCI_STATUS_VAL;
+ if (m->misc)
+ m->status |= MCI_STATUS_MISCV;

- if (i_mce.misc)
- i_mce.status |= MCI_STATUS_MISCV;
-
- if (i_mce.synd)
- i_mce.status |= MCI_STATUS_SYNDV;
+ if (m->synd)
+ m->status |= MCI_STATUS_SYNDV;

if (inj_type == SW_INJ) {
- mce_log(&i_mce);
- return;
+ mce_log(m);
+ return 0;
}

+ if (!hw_injection_possible)
+ return -EINVAL;
+
/* prep MCE global settings for the injection */
mcg_status = MCG_STATUS_MCIP | MCG_STATUS_EIPV;

- if (!(i_mce.status & MCI_STATUS_PCC))
+ if (!(m->status & MCI_STATUS_PCC))
mcg_status |= MCG_STATUS_RIPV;

/*
@@ -556,8 +556,8 @@ static void do_inject(void)
* - MCx_STATUS[UC] cleared: deferred errors are _not_ UC
*/
if (inj_type == DFR_INT_INJ) {
- i_mce.status |= MCI_STATUS_DEFERRED;
- i_mce.status &= ~MCI_STATUS_UC;
+ m->status |= MCI_STATUS_DEFERRED;
+ m->status &= ~MCI_STATUS_UC;
}

/*
@@ -578,13 +578,13 @@ static void do_inject(void)

toggle_hw_mce_inject(cpu, true);

- i_mce.mcgstatus = mcg_status;
- i_mce.inject_flags = inj_type;
- smp_call_function_single(cpu, prepare_msrs, &mce_err, 0);
+ m->mcgstatus = mcg_status;
+ m->inject_flags = inj_type;
+ smp_call_function_single(cpu, prepare_msrs, NULL, 0);

toggle_hw_mce_inject(cpu, false);

- if (mce_err.err)
+ if (inj_desc.err)
goto err;

switch (inj_type) {
@@ -601,6 +601,7 @@ static void do_inject(void)
err:
cpus_read_unlock();

+ return inj_desc.err;
}

/*
@@ -611,6 +612,7 @@ static int inj_bank_set(void *data, u64 val)
{
struct mce *m = (struct mce *)data;
u8 n_banks;
+ int err;
u64 cap;

/* Get bank count on target CPU so we can handle non-uniform values. */
@@ -650,12 +652,12 @@ static int inj_bank_set(void *data, u64 val)
}

inject:
- do_inject();
+ err = do_inject();

/* Reset injection struct */
- setup_inj_struct(&i_mce);
+ setup_inj_struct();

- return mce_err.err;
+ return err;
}

MCE_INJECT_GET(bank);
@@ -745,7 +747,7 @@ static void __init debugfs_init(void)

for (i = 0; i < ARRAY_SIZE(dfs_fls); i++)
debugfs_create_file(dfs_fls[i].name, dfs_fls[i].perm, dfs_inj,
- &i_mce, dfs_fls[i].fops);
+ &inj_desc.m, dfs_fls[i].fops);
}

static int __init inject_init(void)
@@ -758,7 +760,7 @@ static int __init inject_init(void)
register_nmi_handler(NMI_LOCAL, mce_raise_notify, 0, "mce_notify");
mce_register_injector_chain(&inject_nb);

- setup_inj_struct(&i_mce);
+ setup_inj_struct();

pr_info("Machine check injector initialized\n");

diff --git a/arch/x86/kernel/cpu/mce/internal.h b/arch/x86/kernel/cpu/mce/internal.h
index 4ae0e603f7fa..7e03f5b7f6bd 100644
--- a/arch/x86/kernel/cpu/mce/internal.h
+++ b/arch/x86/kernel/cpu/mce/internal.h
@@ -211,7 +211,7 @@ noinstr u64 mce_rdmsrl(u32 msr);

static __always_inline u32 mca_msr_reg(int bank, enum mca_msr reg)
{
- if (mce_flags.smca) {
+ if (cpu_feature_enabled(X86_FEATURE_SMCA)) {
switch (reg) {
case MCA_CTL: return MSR_AMD64_SMCA_MCx_CTL(bank);
case MCA_ADDR: return MSR_AMD64_SMCA_MCx_ADDR(bank);

--
Regards/Gruss,
Boris.