From: Qiuxu Zhuo qiuxu.zhuo@intel.com
[ Upstream commit 20e190b1c1fd88b21cc5106c12cfe6def5ab849d ]
Some BIOS versions may fuse off certain memory controllers and set the registers of these absent memory controllers to ~0. The current igen6_edac mistakenly enumerates these absent memory controllers and registers them with the EDAC core.
Skip the absent memory controllers to avoid mistakenly enumerating them.
Signed-off-by: Qiuxu Zhuo qiuxu.zhuo@intel.com Signed-off-by: Tony Luck tony.luck@intel.com Link: https://lore.kernel.org/r/20250408132455.489046-2-qiuxu.zhuo@intel.com Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES** This commit should be backported to stable kernel trees. Here's my extensive analysis: ## Bug Impact and User Experience This commit fixes a real problem where **some BIOS versions fuse off certain memory controllers** and set their registers to `~0` (all 1s). The current igen6_edac driver mistakenly enumerates these absent memory controllers and registers them with the EDAC core, which can lead to: 1. **Incorrect memory controller enumeration** - showing non-existent memory controllers to userspace 2. **Potential false error reporting** - trying to read error logs from non-existent hardware 3. **Resource waste** - allocating structures and registering devices for hardware that doesn't exist ## Code Analysis - Minimal and Safe Changes Looking at the specific code changes: ### 1. New Detection Function ```c +/* Check whether the memory controller is absent. model/ prompt/ src/ target/ +static bool igen6_imc_absent(void __iomem *window) +{ + return readl(window + MAD_INTER_CHANNEL_OFFSET) == ~0; +} ``` This is a **simple, conservative check** that reads a known register (`MAD_INTER_CHANNEL_OFFSET`) and checks if it returns all 1s (`~0`), which is the standard pattern for absent/fused-off hardware. ### 2. Modified Registration Logic The key change in `igen6_register_mcis()`: ```c + if (igen6_imc_absent(window)) { + iounmap(window); + edac_dbg(2, "Skip absent mc%d\n", pmc); + continue; + } ``` This **safely skips** absent controllers rather than trying to register them. The logic is: - Map the memory controller's MMIO space - Check if it's absent (registers return ~0) - If absent: unmap and continue to next controller - If present: proceed with normal registration ### 3. Robust Error Handling The code maintains proper resource cleanup and adds logging for when fewer controllers are found than expected: ```c + if (lmc < res_cfg->num_imc) + igen6_printk(KERN_WARNING, "Expected %d mcs, but only %d detected.", + res_cfg->num_imc, lmc); ``` ## Comparison with Similar Commits Looking at the historical examples: **Similar Commit #1 (YES)** - "EDAC/i10nm: Skip the absent memory controllers" has nearly identical logic and was backported because it fixed absent memory controller detection causing call traces. **Similar Commit #2 (YES)** - A dependency fix that prevented build errors was backported. This commit follows the same pattern as **Similar Commit #1** - it's a focused bug fix for absent hardware detection with minimal risk. ## Why This Should Be Backported ### 1. **Clear Bug Fix** This addresses a specific, reproducible issue where BIOS configurations cause incorrect driver behavior. ### 2. **Minimal Risk** - Small, contained change - Only affects the memory controller enumeration path - Adds defensive checks rather than changing core logic - Maintains backward compatibility ### 3. **Follows Established Patterns** The "check register for ~0" pattern is well-established in kernel hardware detection and matches the successful backport in Similar Commit #1. ### 4. **Hardware Support Issue** This fixes support for legitimate hardware configurations where BIOS has fused off memory controllers - these systems should work correctly. ### 5. **Stable Tree Criteria Met** - ✅ Fixes important bug affecting users - ✅ Small and contained change - ✅ No architectural changes - ✅ Minimal regression risk - ✅ Confined to single driver subsystem The commit represents exactly the type of targeted hardware fix that stable trees are designed to include - it resolves a real-world compatibility issue with a safe, minimal change.
drivers/edac/igen6_edac.c | 78 +++++++++++++++++++++++++++++++-------- 1 file changed, 62 insertions(+), 16 deletions(-)
diff --git a/drivers/edac/igen6_edac.c b/drivers/edac/igen6_edac.c index 595908af9e5c9..14692c2da6222 100644 --- a/drivers/edac/igen6_edac.c +++ b/drivers/edac/igen6_edac.c @@ -127,6 +127,7 @@
static struct res_config { bool machine_check; + /* The number of present memory controllers. */ int num_imc; u32 imc_base; u32 cmf_base; @@ -1201,23 +1202,21 @@ static void igen6_check(struct mem_ctl_info *mci) irq_work_queue(&ecclog_irq_work); }
-static int igen6_register_mci(int mc, u64 mchbar, struct pci_dev *pdev) +/* Check whether the memory controller is absent. */ +static bool igen6_imc_absent(void __iomem *window) +{ + return readl(window + MAD_INTER_CHANNEL_OFFSET) == ~0; +} + +static int igen6_register_mci(int mc, void __iomem *window, struct pci_dev *pdev) { struct edac_mc_layer layers[2]; struct mem_ctl_info *mci; struct igen6_imc *imc; - void __iomem *window; int rc;
edac_dbg(2, "\n");
- mchbar += mc * MCHBAR_SIZE; - window = ioremap(mchbar, MCHBAR_SIZE); - if (!window) { - igen6_printk(KERN_ERR, "Failed to ioremap 0x%llx\n", mchbar); - return -ENODEV; - } - layers[0].type = EDAC_MC_LAYER_CHANNEL; layers[0].size = NUM_CHANNELS; layers[0].is_virt_csrow = false; @@ -1283,7 +1282,6 @@ static int igen6_register_mci(int mc, u64 mchbar, struct pci_dev *pdev) fail2: edac_mc_free(mci); fail: - iounmap(window); return rc; }
@@ -1309,6 +1307,56 @@ static void igen6_unregister_mcis(void) } }
+static int igen6_register_mcis(struct pci_dev *pdev, u64 mchbar) +{ + void __iomem *window; + int lmc, pmc, rc; + u64 base; + + for (lmc = 0, pmc = 0; pmc < NUM_IMC; pmc++) { + base = mchbar + pmc * MCHBAR_SIZE; + window = ioremap(base, MCHBAR_SIZE); + if (!window) { + igen6_printk(KERN_ERR, "Failed to ioremap 0x%llx for mc%d\n", base, pmc); + rc = -ENOMEM; + goto out_unregister_mcis; + } + + if (igen6_imc_absent(window)) { + iounmap(window); + edac_dbg(2, "Skip absent mc%d\n", pmc); + continue; + } + + rc = igen6_register_mci(lmc, window, pdev); + if (rc) + goto out_iounmap; + + /* Done, if all present MCs are detected and registered. */ + if (++lmc >= res_cfg->num_imc) + break; + } + + if (!lmc) { + igen6_printk(KERN_ERR, "No mc found.\n"); + return -ENODEV; + } + + if (lmc < res_cfg->num_imc) + igen6_printk(KERN_WARNING, "Expected %d mcs, but only %d detected.", + res_cfg->num_imc, lmc); + + return 0; + +out_iounmap: + iounmap(window); + +out_unregister_mcis: + igen6_unregister_mcis(); + + return rc; +} + static int igen6_mem_slice_setup(u64 mchbar) { struct igen6_imc *imc = &igen6_pvt->imc[0]; @@ -1405,7 +1453,7 @@ static void opstate_set(struct res_config *cfg, const struct pci_device_id *ent) static int igen6_probe(struct pci_dev *pdev, const struct pci_device_id *ent) { u64 mchbar; - int i, rc; + int rc;
edac_dbg(2, "\n");
@@ -1421,11 +1469,9 @@ static int igen6_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
opstate_set(res_cfg, ent);
- for (i = 0; i < res_cfg->num_imc; i++) { - rc = igen6_register_mci(i, mchbar, pdev); - if (rc) - goto fail2; - } + rc = igen6_register_mcis(pdev, mchbar); + if (rc) + goto fail;
if (res_cfg->num_imc > 1) { rc = igen6_mem_slice_setup(mchbar);