On 01/03/2025 01:32, Yang Shi wrote:

On 2/28/25 10:24 AM, Mikołaj Lenczewski wrote:

quoted

For supporting BBM Level 2 for userspace mappings, we want to ensure
that the smmu also supports its own version of BBM Level 2. Luckily, the
smmu spec (IHI 0070G 3.21.1.3) is stricter than the aarch64 spec (DDI
0487K.a D8.16.2), so already guarantees that no aborts are raised when
BBM level 2 is claimed.

Add the feature and testing for it under arm_smmu_sva_supported().

Signed-off-by: Mikołaj Lenczewski <redacted>
---
  arch/arm64/kernel/cpufeature.c                  | 7 +++----
  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c | 3 +++
  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c     | 3 +++
  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h     | 4 ++++
  4 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 63f6d356dc77..1022c63f81b2 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c

@@ -2223,8 +2223,6 @@ static bool has_bbml2_noabort(const struct

arm64_cpu_capabilities *caps, int sco
              if (!cpu_has_bbml2_noabort(__cpu_read_midr(cpu)))
                  return false;
          }
-
-        return true;
      } else if (scope & SCOPE_LOCAL_CPU) {
          /* We are a hot-plugged CPU, so only need to check our MIDR.
           * If we have the correct MIDR, but the kernel booted on an

@@ -2232,10 +2230,11 @@ static bool has_bbml2_noabort(const struct

arm64_cpu_capabilities *caps, int sco
           * we have an incorrect MIDR, but the kernel booted on a
           * sufficient CPU, we will not bring up this CPU.
           */
-        return cpu_has_bbml2_noabort(read_cpuid_id());
+        if (!cpu_has_bbml2_noabort(read_cpuid_id()))
+            return false;
      }
  -    return false;
+    return has_cpuid_feature(caps, scope);

Do we really need this? IIRC, it means the MIDR has to be in the allow list
*AND* MMFR2 register has to be set too. AmpereOne doesn't have MMFR2 register set.

Miko, I think this should have been squashed into patch #1? It doesn't belong in
this patch.

Yang, we discussed this internally and decided that we thought it was best to
still require BBML2 being advertised in the feature register. That way if trying
to use KVM to emulate a CPU that is in the allow list but doesn't really support
BBML2, we won't try to use it.

But we still end up with the same problem if running on a physical CPU that
supports BBML2 with conflict aborts, but emulating a CPU in the allow list. So
given AmpereOne doesn't advertise BBML2 but does support it, I'd be happy to
remove this check.

Thanks,
Ryan

Thanks,
Yang

quoted

  }
    #ifdef CONFIG_ARM64_PAN

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c b/drivers/iommu/

arm/arm-smmu-v3/arm-smmu-v3-sva.c
index 9ba596430e7c..6ba182572788 100644

--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c

@@ -222,6 +222,9 @@ bool arm_smmu_sva_supported(struct arm_smmu_device *smmu)

          feat_mask |= ARM_SMMU_FEAT_VAX;
      }
  +    if (system_supports_bbml2_noabort())
+        feat_mask |= ARM_SMMU_FEAT_BBML2;
+
      if ((smmu->features & feat_mask) != feat_mask)
          return false;
  diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/
arm/arm-smmu-v3/arm-smmu-v3.c
index 358072b4e293..dcee0bdec924 100644

--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

@@ -4406,6 +4406,9 @@ static int arm_smmu_device_hw_probe(struct

arm_smmu_device *smmu)
      if (FIELD_GET(IDR3_RIL, reg))
          smmu->features |= ARM_SMMU_FEAT_RANGE_INV;
  +    if (FIELD_GET(IDR3_BBML, reg) == IDR3_BBML2)
+        smmu->features |= ARM_SMMU_FEAT_BBML2;
+
      /* IDR5 */
      reg = readl_relaxed(smmu->base + ARM_SMMU_IDR5);
  diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/
arm/arm-smmu-v3/arm-smmu-v3.h
index bd9d7c85576a..85eaf3ab88c2 100644

--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h

@@ -60,6 +60,9 @@ struct arm_smmu_device;

  #define ARM_SMMU_IDR3            0xc
  #define IDR3_FWB            (1 << 8)
  #define IDR3_RIL            (1 << 10)
+#define IDR3_BBML            GENMASK(12, 11)
+#define IDR3_BBML1            (1 << 11)
+#define IDR3_BBML2            (2 << 11)
    #define ARM_SMMU_IDR5            0x14
  #define IDR5_STALL_MAX            GENMASK(31, 16)

@@ -754,6 +757,7 @@ struct arm_smmu_device {

  #define ARM_SMMU_FEAT_HA        (1 << 21)
  #define ARM_SMMU_FEAT_HD        (1 << 22)
  #define ARM_SMMU_FEAT_S2FWB        (1 << 23)
+#define ARM_SMMU_FEAT_BBML2        (1 << 24)
      u32                features;
    #define ARM_SMMU_OPT_SKIP_PREFETCH    (1 << 0)