Re: [PATCH 3/3] x86/MCE/AMD: Get address from already initialized block

Borislav Petkov
2018-05-17T10:41:48Z

On Thu, May 17, 2018 at 08:49:31AM +0200, Johannes Hirte wrote:
> Maybe I'm missing something, but those RDMSR IPSs don't happen on
> pre-SMCA systems, right? So the caching should be avoided here, cause
> the whole lookup looks more expensive to me than the simple switch-block
> in get_block_address.

Yeah, and we should simply cache all those MSR values as I suggested then.

The patch at the end should fix your issue.

Yazen, so I'm working on the assumption that all addresses are the same
on every core - I dumped them and it looks like this:

128 bank: 00, block: 0 : 0xc0002003
128 bank: 00, block: 1 : 0x0
128 bank: 01, block: 0 : 0xc0002013
128 bank: 01, block: 1 : 0x0
128 bank: 02, block: 0 : 0xc0002023
128 bank: 02, block: 1 : 0x0
128 bank: 03, block: 0 : 0xc0002033
128 bank: 03, block: 1 : 0x0
128 bank: 04, block: 0 : 0x0
128 bank: 05, block: 0 : 0xc0002053
128 bank: 05, block: 1 : 0x0
128 bank: 06, block: 0 : 0xc0002063
128 bank: 06, block: 1 : 0x0
128 bank: 07, block: 0 : 0xc0002073
128 bank: 07, block: 1 : 0x0
128 bank: 08, block: 0 : 0xc0002083
128 bank: 08, block: 1 : 0x0
128 bank: 09, block: 0 : 0xc0002093
128 bank: 09, block: 1 : 0x0
128 bank: 10, block: 0 : 0xc00020a3
128 bank: 10, block: 1 : 0x0
128 bank: 11, block: 0 : 0xc00020b3
128 bank: 11, block: 1 : 0x0
128 bank: 12, block: 0 : 0xc00020c3
128 bank: 12, block: 1 : 0x0
128 bank: 13, block: 0 : 0xc00020d3
128 bank: 13, block: 1 : 0x0
128 bank: 14, block: 0 : 0xc00020e3
128 bank: 14, block: 1 : 0x0
128 bank: 15, block: 0 : 0xc00020f3
128 bank: 15, block: 1 : 0x0
128 bank: 16, block: 0 : 0xc0002103
128 bank: 16, block: 1 : 0x0
128 bank: 17, block: 0 : 0xc0002113
128 bank: 17, block: 1 : 0x0
128 bank: 18, block: 0 : 0xc0002123
128 bank: 18, block: 1 : 0x0
128 bank: 19, block: 0 : 0xc0002133
128 bank: 19, block: 1 : 0x0
128 bank: 20, block: 0 : 0xc0002143
128 bank: 20, block: 1 : 0x0
128 bank: 21, block: 0 : 0xc0002153
128 bank: 21, block: 1 : 0x0
128 bank: 22, block: 0 : 0xc0002163
128 bank: 22, block: 1 : 0x0

so you have 128 times the same address on a 128 core Zen box.

If that is correct, then we can use this nice simplification and cache
them globally and not per-CPU. Seems to work here. Scream if something's
amiss.

Thx.

---
>From d8614e904d8f63b89d2d204d6fa247c4c416a1b6 Mon Sep 17 00:00:00 2001
From: Borislav Petkov <bp@susede>
Date: Thu, 17 May 2018 10:46:26 +0200
Subject: [PATCH] array caching

Not-Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/kernel/cpu/mcheck/mce_amd.c | 29 ++++++++++++++--------------
1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c b/arch/x86/kernel/cpu/mcheck/mce_amd.c
index f7666eef4a87..c8e038800591 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
@@ -94,6 +94,11 @@ static struct smca_bank_name smca_names[] = {
[SMCA_SMU] = { "smu", "System Management Unit" },
};

+static u32 smca_bank_addrs[MAX_NR_BANKS][NR_BLOCKS] __ro_after_init =
+{
+ [0 ... MAX_NR_BANKS - 1] = { [0 ... NR_BLOCKS - 1] = -1 }
+};
+
const char *smca_get_name(enum smca_bank_types t)
{
if (t >= N_SMCA_BANK_TYPES)
@@ -443,20 +448,26 @@ static u32 smca_get_block_address(unsigned int cpu, unsigned int bank,
if (!block)
return MSR_AMD64_SMCA_MCx_MISC(bank);

+ /* Check our cache first: */
+ if (smca_bank_addrs[bank][block] != -1)
+ return smca_bank_addrs[bank][block];
+
/*
* For SMCA enabled processors, BLKPTR field of the first MISC register
* (MCx_MISC0) indicates presence of additional MISC regs set (MISC1-4).
*/
if (rdmsr_safe_on_cpu(cpu, MSR_AMD64_SMCA_MCx_CONFIG(bank), &low, &high))
- return addr;
+ goto out;

if (!(low & MCI_CONFIG_MCAX))
- return addr;
+ goto out;

if (!rdmsr_safe_on_cpu(cpu, MSR_AMD64_SMCA_MCx_MISC(bank), &low, &high) &&
(low & MASK_BLKPTR_LO))
- return MSR_AMD64_SMCA_MCx_MISCy(bank, block - 1);
+ addr = MSR_AMD64_SMCA_MCx_MISCy(bank, block - 1);

+out:
+ smca_bank_addrs[bank][block] = addr;
return addr;
}

@@ -468,18 +479,6 @@ static u32 get_block_address(unsigned int cpu, u32 current_addr, u32 low, u32 hi
if ((bank >= mca_cfg.banks) || (block >= NR_BLOCKS))
return addr;

- /* Get address from already initialized block. */
- if (per_cpu(threshold_banks, cpu)) {
- struct threshold_bank *bankp = per_cpu(threshold_banks, cpu)[bank];
-
- if (bankp && bankp->blocks) {
- struct threshold_block *blockp = &bankp->blocks[block];
-
- if (blockp)
- return blockp->address;
- }
- }
-
if (mce_flags.smca)
return smca_get_block_address(cpu, bank, block);

--
2.17.0.391.g1f1cddd558b5

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