Since upstream commit 923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9
("x86/resctrl: Query LLC monitoring properties once during boot"),
resctrl_cpu_detect() has been moved from common cpu initialization
code to vendor-specific bsp init helper, while hygon didn't put
that call in their code.

This triggers div-zero fault during early booting stage on our
machines with X86_FEATURE_CQM* supported, where
get_rdt_mon_resources() tries to calculate mon_l3_config with
uninitialized boot_cpu_data.x86_cache_occ_scale.

Fix the missing resctrl_cpu_detect() in hygon bsp init helper.

Signed-off-by: Tianxiang Peng <txpeng@tencent.com>
Reviewed-by: Hui Li <caelli@tencent.com>
---
 arch/x86/kernel/cpu/hygon.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/cpu/hygon.c b/arch/x86/kernel/cpu/hygon.c
index 9f914bf80180..5f73bad0b9fd 100644
--- a/arch/x86/kernel/cpu/hygon.c
+++ b/arch/x86/kernel/cpu/hygon.c
@@ -16,6 +16,7 @@
 #include <asm/page.h>
 #include <linux/module.h>
 #include <linux/init.h>
+#include <asm/resctrl.h>
 
 #ifdef CONFIG_X86_64
 # include <asm/set_memory.h>
@@ -271,6 +272,8 @@ static void bsp_init_hygon(struct cpuinfo_x86 *c)
 			x86_amd_ls_cfg_ssbd_mask = 1ULL << 10;
 		}
 	}
+
+	resctrl_cpu_detect(c);
 }
 
 static void early_init_hygon(struct cpuinfo_x86 *c)
-- 
2.43.5

On Mon, Jun 23, 2025 at 05:31:53PM +0800, Tianxiang Peng wrote:
> Since upstream commit 923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9
> ("x86/resctrl: Query LLC monitoring properties once during boot"),

This commit is in 5.7.

You notice the issue only now because you were on an old kernel before and
moved to 5-something, which is >= 5.7?

> resctrl_cpu_detect() has been moved from common cpu initialization
> code to vendor-specific bsp init helper, while hygon didn't put
> that call in their code.
> 
> This triggers div-zero fault during early booting stage on our
> machines with X86_FEATURE_CQM* supported, where
> get_rdt_mon_resources() tries to calculate mon_l3_config with
> uninitialized boot_cpu_data.x86_cache_occ_scale.
> 
> Fix the missing resctrl_cpu_detect() in hygon bsp init helper.
> 
> Signed-off-by: Tianxiang Peng <txpeng@tencent.com>

Your From: is Tianxiang Peng <luminosity1999@gmail.com> and that will appear
in git as author.

Do you want it to be the email address you have in the Signed-off-by instead?
I.e., your company.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Thank you for your feedback, I'm sorry for the delayed response.

On Mon, 23 Jun 2025 15:31:17 +0200, Borislav Petkov wrote:
> > Since upstream commit 923f3a2b48bdccb6a1d1f0dd48de03de7ad936d9
> > ("x86/resctrl: Query LLC monitoring properties once during boot"),
> 
> This commit is in 5.7.
> 
> You notice the issue only now because you were on an old kernel before and
> moved to 5-something, which is >= 5.7?

The issue surfaced when we migrated our 5.15-based kernel to new Hygon machines
supporting X86_FEATURE_CQM*. Our older Hygon hardware lacks this capability
(manually verified).

To confirm the behavior:
- On new Hygon machines, both 5.15 and 6.15 kernels trigger the div-zero fault.
- Applying the patch resolves the issue consistently.

On Mon, 23 Jun 2025 15:31:17 +0200, Borislav Petkov wrote:
> > resctrl_cpu_detect() has been moved from common cpu initialization
> > code to vendor-specific bsp init helper, while hygon didn't put
> > that call in their code.
> > 
> > This triggers div-zero fault during early booting stage on our
> > machines with X86_FEATURE_CQM* supported, where
> > get_rdt_mon_resources() tries to calculate mon_l3_config with
> > uninitialized boot_cpu_data.x86_cache_occ_scale.
> > 
> > Fix the missing resctrl_cpu_detect() in hygon bsp init helper.
> > 
> > Signed-off-by: Tianxiang Peng <txpeng@tencent.com>
> 
> Your From: is Tianxiang Peng <luminosity1999@gmail.com> and that will appear
> in git as author.
> 
> Do you want it to be the email address you have in the Signed-off-by instead?
> I.e., your company.

Apologies for the gmail sender address, corporate network constraints require this
workaround. For the git author, I'd appreciate using my company email(txpeng@tencent.com)
instead.

Regards,
Tianxiang Peng

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     d8df126349dad855cdfedd6bbf315bad2e901c2f
Gitweb:        https://git.kernel.org/tip/d8df126349dad855cdfedd6bbf315bad2e901c2f
Author:        Tianxiang Peng <txpeng@tencent.com>
AuthorDate:    Mon, 23 Jun 2025 17:31:53 +08:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Mon, 18 Aug 2025 12:09:26 +02:00

x86/cpu/hygon: Add missing resctrl_cpu_detect() in bsp_init helper

Since

  923f3a2b48bd ("x86/resctrl: Query LLC monitoring properties once during boot")

resctrl_cpu_detect() has been moved from common CPU initialization code to
the vendor-specific BSP init helper, while Hygon didn't put that call in their
code.

This triggers a division by zero fault during early booting stage on our
machines with X86_FEATURE_CQM* supported, where get_rdt_mon_resources() tries
to calculate mon_l3_config with uninitialized boot_cpu_data.x86_cache_occ_scale.

Add the missing resctrl_cpu_detect() in the Hygon BSP init helper.

  [ bp: Massage commit message. ]

Fixes: 923f3a2b48bd ("x86/resctrl: Query LLC monitoring properties once during boot")
Signed-off-by: Tianxiang Peng <txpeng@tencent.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Hui Li <caelli@tencent.com>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/20250623093153.3016937-1-txpeng@tencent.com
---
 arch/x86/kernel/cpu/hygon.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/cpu/hygon.c b/arch/x86/kernel/cpu/hygon.c
index 2154f12..1fda6c3 100644
--- a/arch/x86/kernel/cpu/hygon.c
+++ b/arch/x86/kernel/cpu/hygon.c
@@ -16,6 +16,7 @@
 #include <asm/spec-ctrl.h>
 #include <asm/delay.h>
 #include <asm/msr.h>
+#include <asm/resctrl.h>
 
 #include "cpu.h"
 
@@ -117,6 +118,8 @@ static void bsp_init_hygon(struct cpuinfo_x86 *c)
 			x86_amd_ls_cfg_ssbd_mask = 1ULL << 10;
 		}
 	}
+
+	resctrl_cpu_detect(c);
 }
 
 static void early_init_hygon(struct cpuinfo_x86 *c)